game-state-management-monogame
A direct port of the Game State Management sample for XNA 4 that used to be found here to Monogame. It seems to have since been moved or deleted, but please keep in mind the license that used to be noted at that link (or wherever it might be now...).
There is a very good XNA Game Studio Archive repo that has a lot of XNA Game Studio education content, if you need more of a reference
This is currently working while targeting netcoreapp3.1 and the version of Monogame that comes with the template found here - MonoGame (.NET Core)