Even after the latest Windows 10 update that enabled turning vsync off for UWP applications, I’m still unable to record matches using the Xbox app.
Before the update Win + Alt + G simply didn’t work, warning that this game doesn’t allow recording videos. After this update I can record videos but they don’t actually capture the screen.
Other UWP games work as usual, it’s just KI that refuses to be recorded. I tested both windowed and (pseudo) full screen modes.
Here’s an example: