I have UBlock installed on Firefox and what is pictured here is what has been happening for every video that I’m clicking on. Panning doesn’t make the video play either. I tried that. It’s not my internet connection since the videos and ads that you can’t even skip and pause when you tab out play just fine on Chrome. In the days before this happened I got several popups from YouTube saying that adblockers aren’t allowed after months of browsing YouTube ad-free without issue
I find that often the player will spin like this for 10-20 secs before starting to play. I wonder if it’s trying to play an ad, and the ad is being successfully blocked but the video doesn’t start until the length of the ad is over. If you see the black screen and the loading spinner, try just waiting for 30 secs and seeing if it starts on its own.