Have you tried using Window Capture, and then select the open PP presentation?
I don't own a M1 MBP, I'm on a classic MacBook Pro, and I also haven't PP as a source, but use Window Capture to do it.
A neat trick when doing so is to configure the presentation mode to "Window", that way, your screen won't be filled with a presentation, but instead appear in a window by itself.
HTH,
-Tom