It's not consistent but they do block users [0] when adblock is detected. I wonder how it goes internally and what's the actual reason that stops them for doing it full scale, but I've personally got the block so can confirm it's a real thing, and assume they won't be giving it up (of course workarounds also exist)

[0] https://www.techspot.com/news/107221-youtube-anti-ad-blocker...