I found this topic while searching for same issue. I confirm that I have the same issue as OP described word by word. As a plus It seems video always starts few seconds infront of sound as frozen. After sound sync up with video they run together.
Device : SM-G991B/DS ( S21 5G Exynos )
Android 12 / OneUI 4.1 / Youtube 17.15.33
Hallo ! I have exactly same issue!
After software update for Samsung s21 ultra I noticed that YouTube videos and shorts getting freezing but sound goes normal and after 2-5 seconds when it synchronise it goes normal....
My wife have exactly same phone and I watched YouTube on her phone and exactly same issue after a phone software update.
Pretty annoying.... please fix this samsung