I was hit with this ominous popup for the first time this morning, and then every time I clicked a video. I'm using Firefox with the uBlock Origin and Enhancer for YouTube extensions, by the way.
While previously they had this popup with a close button, then they added a timer to the close button, now they're saying the video player will be blocked after three videos if I don't disable ad blocking. That's quite the escalation!
So I did the sensible thing: I cleared the cache in uBlock Origin and fetched the latest blocklists.
EDIT: If you're still having trouble, follow this guide: https://old.reddit.com/r/uBlockOrigin/comments/173jmog/youtube_antiadblock_and_ads_october_09_2023/