I currently have a 7900XTX with a 7800X3D in my System, and when i play a game on my main Monitor it starts to flicker, when playing a video. This happens on a second Monitor and on the same one, when the game is alt-tabbed.
I tried turning off HDR, Freesync, Enhanced Sync, downclocking the GPU, reinstalling Drivers, turning off MPO, setting my second monitor to 120 Hz (From 144) so its cleanly divided with my first monitor (240Hz), casual Troubleshooting etc.
The Flickering shows as a segment of the Video popping up for a very short duration throughout the whole monitor.