Someone in the Fediverse (I don't know where and who) posted that you have to add the following filters into U-Block Origin. When done you shouldn't see any anti-adblock-warnings :

youtube.com##+js(set,yt.config_.openPopupConfig.supportedPopups.adBlockMessageViewModel,false)

youtube.com##+js(set,Object.prototype.adBlocksFound,O)

youtube.com##+js(set,ytplayer.config.aras.raw_player_response.adPlacements,[])

youtube.com##+js(set,Object.prototype.hasAllowedlnstreamAd,true)

I might add that I haven't experienced any anti-adblock-warnings yet, but I added these filters in advance. I might be worth a shot!