FYI YouTube is currently waging war against Brave’s built-in ad-block and/or a Chrome plugin I use to block YouTube ads. For the last couple of days I’ve gotten that black screen too… for 30-40 seconds when ads apparently would be playing.
So I’m guessing you are using some sort of ad-block extensions with your browsers, and YouTube is recognizing it on that one account of yours.
So I’d wait for a while to see if the videos appear as they did with me.
Generally speaking I’d make sure I was running the latest versions of the browsers, and I’d delete cache and cookie, and restart the Mac, and try the browser without plugins (specifically ad-block) and see if that helps. If it does re-enable plugins and see what happens.