I found a Bug, when you try to open the full screen at youtube video, brave asking if you permit this action, if you say permit the video expand normally, but, if you deny this action the video is capture and continue in the same box video but xpand a part inside (is like a zoom in a corner). I think this result caused by the environment with the tab motion. Anyways, it is something to be fixed.
And this happen when you want full screen but, you say Deny:
Update Channel dev
OS Platform macOS
OS Release 16.6.0
OS Architecture x64