I already made a review on the opera webshop, but maybe here you look more often.
I like it very much but apparently there is a multi plugin issue. I'm using it along with YouTube Anti Translate(I cannot add url, so replace spaces with dots: addons mozilla org/en-US/firefox/addon/youtube-anti-translate/) and Clickbait Remover for Youtube(addons mozilla org/en-US/firefox/addon/clickbait-remover-for-youtube). When all of three are on, the video page will freeze. If I disable just any of those, it starts working. I tried multiple browsers, chromium and firefox based. Of course the greatest burden is You Tube Anti Translate, but the youtube still works with it and one more plugin. Hopefully you can find the issue.

Stopped working with Youtube today, but I installed a beta version uBlock Origin 1.64.1b2
available on github which seems to be working.

i turned off "Parse and enforce cosmetic filters" in the filter list setting and youtube worked again.

Loved it until it stopped working today on Youtube.

Youtube today showed in firefox: Ad blockers are not allowed on Youtube. I was able to X it away, but I'm in fear of my account being removed.

Adguard just dropped the ball. They now limit the number of filters you can use. uBlock is good but not the most effective in blocking annoyances and stubborn cookie notifications.

Ghostery is the next best option or Brave but I have some doubts it won't be forced to move to MV3. Otherwise, the trend is to move toward a hybrid/Fork Chrome browser or a FireFox clone. Regular FF is too slow, heavy on CPU use, and writes more in the background than other browsers.