Mate, I'm quite surprised by this because I just tested it again and it works as expected.
In case it helps, here are the exact steps I took.
- Open Visual Studio 2017
- Create a "MonoGame Windows Project" (from the templates installed with MonoGame)
- Check that it compiles and runs
- Change the target framework to .NET Framework 4.7.2
- Install MonoGame.Extended (using the NuGet package manager GUI)
- Draw a rectangle (to make sure Extended is working)
spriteBatch.FillRectangle(100, 100, 200, 300, Color.Red);
That's pretty much all there is to it. I'm not sure what you're doing differently.
Some things to try:
- Check that you've got the latest versions of everything (Visual Studio updates, .NET Framework, etc)
- Maybe you're using and old version of NuGet
- Clone the source and see if you can get the demos to work
- Maybe try the .NET Core way