I just ran into this (using MonoGame for the first time), but found a fix.
Apparently this happens when iOS doesn't think your app can support the larger, "newer" device resolutions.
This can be fixed by making sure your launch screen configuration supports larger resolutions.
One way to fix it:
- Add new file to your iOS Project:
Launch Screen (C#) named
Info.plist, under "iPhone Launch Images", set "Launch Screen:" to
Next time I ran, (I had to do a Clean project first for some reason,) it displayed fullscreen finally.