Oh interesting, I just looked into it and apparently it requires the app to support it. Apps like Keynote, Zoom, Slack, Facetime and Teams Classic (but not "new Teams") all support it. That's really strange imo, you'd think the OS would just add the overlay to the video signal and pass it through to the app. I wonder why it's implemented this way. The other OS-level video features like portrait mode, studio lighting, reactions and center stage don't require support from the app at all.