Trying to build Monogame from source on Windows 10 fails

Trying to build the MonoGame.Framework.WindowsDX solution and it is failing for both projects in the solution.
Some of the error messages are:

1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\Texture2D.StbSharp.cs(5,7,5,20): error CS0246: The type or namespace name 'StbImageSharp' could not be found (are you missing a using directive or an assembly reference?)

1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\Texture2D.StbSharp.cs(6,7,6,25): error CS0246: The type or namespace name ‘StbImageWriteSharp’ could not be found (are you missing a using directive or an assembly reference?)
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Audio\SoundEffect.XAudio.cs(31,32,31,40): warning CS3021: ‘SoundEffect.Speakers’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Color.cs(177,16,177,21): warning CS3021: ‘Color.Color(uint)’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Game.cs(331,27,331,33): warning CS3021: ‘Game.Window’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Color.cs(1801,23,1801,34): warning CS3021: ‘Color.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Alpha8.cs(20,21,20,32): warning CS3021: ‘Alpha8.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Short4.cs(65,22,65,33): warning CS3021: ‘Short4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgr565.cs(47,23,47,34): warning CS3021: ‘Bgr565.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Short2.cs(35,15,35,26): warning CS3021: ‘Short2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rgba64.cs(18,16,18,27): warning CS3021: ‘Rgba64.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rgba1010102.cs(19,21,19,32): warning CS3021: ‘Rgba1010102.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgra4444.cs(49,23,49,34): warning CS3021: ‘Bgra4444.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgra5551.cs(19,23,19,34): warning CS3021: ‘Bgra5551.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\RenderTargetCube.DirectX.cs(89,33,89,52): warning CS3021: ‘RenderTargetCube.GetRenderTargetView(int)’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\RenderTargetCube.DirectX.cs(96,33,96,52): warning CS3021: ‘RenderTargetCube.GetDepthStencilView()’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rg32.cs(18,21,18,32): warning CS3021: ‘Rg32.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Byte4.cs(65,21,65,32): warning CS3021: ‘Byte4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedShort4.cs(35,22,35,33): warning CS3021: ‘NormalizedShort4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedShort2.cs(35,21,35,32): warning CS3021: ‘NormalizedShort2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedByte4.cs(35,21,35,32): warning CS3021: ‘NormalizedByte4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedByte2.cs(35,23,35,34): warning CS3021: ‘NormalizedByte2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfSingle.cs(19,23,19,34): warning CS3021: ‘HalfSingle.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfVector4.cs(79,22,79,33): warning CS3021: ‘HalfVector4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfVector2.cs(53,21,53,32): warning CS3021: ‘HalfVector2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>Done building project “MonoGame.Framework.WindowsDX.csproj” – FAILED.
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\Texture2D.StbSharp.cs(5,7,5,20): error CS0246: The type or namespace name ‘StbImageSharp’ could not be found (are you missing a using directive or an assembly reference?)
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\Texture2D.StbSharp.cs(6,7,6,25): error CS0246: The type or namespace name ‘StbImageWriteSharp’ could not be found (are you missing a using directive or an assembly reference?)
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Audio\SoundEffect.XAudio.cs(31,32,31,40): warning CS3021: ‘SoundEffect.Speakers’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Color.cs(177,16,177,21): warning CS3021: ‘Color.Color(uint)’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Color.cs(1801,23,1801,34): warning CS3021: ‘Color.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Game.cs(331,27,331,33): warning CS3021: ‘Game.Window’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Short4.cs(65,22,65,33): warning CS3021: ‘Short4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Short2.cs(35,15,35,26): warning CS3021: ‘Short2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rgba64.cs(18,16,18,27): warning CS3021: ‘Rgba64.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rgba1010102.cs(19,21,19,32): warning CS3021: ‘Rgba1010102.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Rg32.cs(18,21,18,32): warning CS3021: ‘Rg32.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedShort4.cs(35,22,35,33): warning CS3021: ‘NormalizedShort4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedShort2.cs(35,21,35,32): warning CS3021: ‘NormalizedShort2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedByte4.cs(35,21,35,32): warning CS3021: ‘NormalizedByte4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\NormalizedByte2.cs(35,23,35,34): warning CS3021: ‘NormalizedByte2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfVector4.cs(79,22,79,33): warning CS3021: ‘HalfVector4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Alpha8.cs(20,21,20,32): warning CS3021: ‘Alpha8.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfVector2.cs(53,21,53,32): warning CS3021: ‘HalfVector2.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\RenderTargetCube.DirectX.cs(89,33,89,52): warning CS3021: ‘RenderTargetCube.GetRenderTargetView(int)’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Platform\Graphics\RenderTargetCube.DirectX.cs(96,33,96,52): warning CS3021: ‘RenderTargetCube.GetDepthStencilView()’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\HalfSingle.cs(19,23,19,34): warning CS3021: ‘HalfSingle.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgr565.cs(47,23,47,34): warning CS3021: ‘Bgr565.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Byte4.cs(65,21,65,32): warning CS3021: ‘Byte4.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgra4444.cs(49,23,49,34): warning CS3021: ‘Bgra4444.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>D:\monogamebuild\MonoGame\MonoGame.Framework\Graphics\PackedVector\Bgra5551.cs(19,23,19,34): warning CS3021: ‘Bgra5551.PackedValue’ does not need a CLSCompliant attribute because the assembly does not have a CLSCompliant attribute
1>Done building project “MonoGame.Framework.WindowsDX.csproj” – FAILED.
2>------ Build started: Project: MonoGame.Tests.WindowsDX, Configuration: Debug Any CPU ------
2>C:\Program Files\dotnet\sdk\3.1.403\Sdks\Microsoft.NET.Sdk.WindowsDesktop\targets\Microsoft.NET.Sdk.WindowsDesktop.targets(96,5): warning NETSDK1106: Microsoft.NET.Sdk.WindowsDesktop requires ‘UseWpf’ or ‘UseWindowsForms’ to be set to ‘true’
2>CSC : error CS0006: Metadata file ‘D:\monogamebuild\MonoGame\Artifacts\MonoGame.Framework\WindowsDX\Debug\netcoreapp3.1\MonoGame.Framework.dll’ could not be found
2>Done building project “MonoGame.Tests.WindowsDX.csproj” – FAILED.
========== Build: 0 succeeded, 2 failed, 0 up-to-date, 0 skipped ==========

StbImageSharp is a 3rd party dependency that should be in the ThirdParty/StbImageSharp folder. Did you follow the build instructions in the readme , specifically did you update the submodules?

git submodule update --init