Looks like you have Use graphics acceleration when available turned OFF, for now. (My screenshot, has it ON. That is preferred, IMHO.)
Suggestion: Scroll down this webpage of your issue/topic and study what may relate … in the Related portion.
More:
‘YouTube Videos weirdly stutter in the first ~1-2 seconds and then continue playing normally’
‘Hardware Acceleration - Video stuttering/Buffering’
‘Youtube has video playback stutter every few seconds unless captions are enabled’
‘YouTube extremely laggy on macOS in Brave (scrolling and video stutter, works fine in Safari)’