Youtube is known for AB testing and regional rollout. I was fine on firefox + ubo until i wasn’t anymore. Until ubo kills it for good, a daily manual filter update fixes it.
Install tampermonkey extension, which lets you install user scripts. Links are on the page. Install the user script that de-fucks youtube on that page. Counterintuitivly, whitelist YouTube in ublock origin. Make sure you arent running anything else that also adblocks, like "enhancer for YouTube." If so, disable their adblock too.
Install firefox for best results. Not for this, just in general.
be careful with weird workarounds like this because as ublock finds ways to hide itself better you'll only make yourself stand out and be a lot more detectable. and as you throw workaround on workaround they'll eventually start conflicting in weird ways which will break things either subtly or very blatantly (which will result in you installing more weird workarounds to try to fix all this which will only make it worse)
the best fix is really to:
switch to latest firefox
keep ublock origin and it's filterlists updated
do not stack any other blockers (including enhancer for youtube or privacy extensions or whatever)
the only exception i'd recommend is https://github.com/AdguardTeam/AdGuardExtra which is specially designed to not conflict with ad blockers like uBO, but even then don't use it if things are working fine without it
regularly clean up the weird workarounds you installed
or just don't install them and wait for ubo to do it's thing considering you'll probably forget about this step