@leocg So the thing happening on my end is that:
When I press the F key it goes into full screen mode but the video starts lagging and buffering. The audio continues to play but the video starts buffering (shows the big loading thing while the audio continues to play in the background.
On exiting full screen the video comes back to normal.
My opera version is:
CORE: 117.0.5408.162 (LEVEL 6)