I have this problem just a day or two ago. Opera's built in youtube ad blocker does not work anymore, because youtube updated block detection, it has the 3 video warning, after 3 videos, cannot load any video at all. I checked Brave and is working fine there, because they always gets it working.
When Opera's blocker is working, it does not often block ads, it is a bit faulty. you see the ads yellow bar but no video.
I switched to ublock and it works like Brave