They have just set up this webpage according to the announcement on one of their dev blogs. Of course there’s irony that they include MonoGame, because if it hadn’t been for MonoGame, all of the XNA library code would have been lost. XNA was Microsoft’s own game development technology that got to version 4 and was then abandoned.
There’s also a page of tutorials teaching Godot, Unity and a backend service called PlayFab. It never ceases to amaze me that Microsoft don’t invest just a little bit more into their games development. They’ve got lots of different platforms including various XBox consoles, PCs, Mobile and so on that can all be programmed using Microsoft related technologies using Microsoft supplied software that is very good and often free. It often feels like they’ve backed off from the days when they were publishing games.