Youtube videos in Safari are cropped in full screen

Youtube videos Safari are cropped in full screen. This does not happen e.g. in Firefox

I'm not a 100% sure, but it seems that this issue started when I recently updated to Version 12.3.1 (21E258)

Here's a screenshot of the video not in full screen mode (the elbow on the right is in the frame):

And here's a screenshot of the same scene in full screen (the elbow on the right is not fully in the frame):