Seems like YouTube might be joining in the social media shakedowns and requiring people to turn off ad blockers to watch YouTube, if it shows up for you, stick this in uBlock Origin:
! YouTube blocker blocker
youtube.com##+js(set, yt.config_.openPopupConfig.supportedPopups.adBlockMessageViewModel, false)
youtube.com##+js(set, Object.prototype.adBlocksFound, 0)
youtube.com##+js(set, ytplayer.config.args.raw_player_response.adPlacements, [])
youtube.com##+js(set, Object.prototype.hasAllowedInstreamAd, true)
(I didn't come up with this, a friend of mine posted it, and I'm pretty sure they didn't make it either lol)