I’ve pinned this topic to avoid confusion and future posts about missing .sln / .csproj files.
The MonoGame project needs generating in order to use it now, just run “ProtoBuild.exe” when cloning / updating the repo.
BE SURE NOT TO CHECK IN .SLN/.CSPROJ files in future pr’s as they will not be accepted.
#ref Where is the MonoGame Framework WindowsPhone csproj file