According to /r/youtube, the fix is to uncheck "uBlock filters - Quick Fixes" in the uBlock preferences under Fliter lists > Built-in
ublock is working for me atm, so I assume its a new round of youtube trying something then ublock countering it.
Just got this message for the first time today looks like they are cracking down hard on adblockers now.
I've been getting these messages multiple times a day with my adblocker disabled. They're practically making YouTube unusable just to get a few more people to disable adblock. I really should go back to just opening tabs with a redirect-to-invidious extension, or maybe I'll take the plunge and install FreeTube.
My Youtube-DL seems non-functional for the past week, usually it's patched back to working after a day or so. I wonder if it actually works but they're targeting VPN addresses more now