As pointed out in the latest Windows 11 Version 24H2 update post, OS build 26100.4946 (which launched on August 12) has ...

What is OBS Open Broadcaster Software, more commonly known as OBS, is a free, open-source software that allows you to record your screen or live-stream the contents of your screen.

You can then use it with streaming software, like OBS, so you can overlay your face on your video stream.

OBS, the streaming software, sees that mirrored screen on your computer and uses it as a source for your stream, like a camera. So, people watching your stream, see what's happening on your phone!