I’m not sure if this works anymore but I saved this message a while back. If you get this pop-up then put this into your adblock custom rules and it should sort it out:

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)