Mageia apparently (sometimes?) auto generates an xorg.conf, that sort of thing doesn't usually work well on my hardware when I've encountered it, although not in a subtle way.
https://wiki.mageia.org/en/Mageia_7_Errata
I tried uninstalling VLC and it's deps so PM was the only video player (although I did have ffmpeg and some other video related things I suppose) and it still kept playing You Tube vids

Looking at the PM dev tools console (my new thing to do) while playing a YouTube video with some ads it seemed to "generate" the content, then again at the start of the video proper:
https://www.youtube.com/generate_204 [HTTP/2.0 204 No Content 134ms]
So I suppose it makes a video stream according to what spec it thinks you want, based on what is detected, and the ads are done separately. Probably best to take advice from the others who might have more useful suggestions.