Most estimates are around 30% for people who use ad blockers. I would guess half or more of those are probably people who had someone else install the ad blocker for them (I personally do it for any family who has me help with their computer) and don’t even care about blocking ads. Half of the remaining half would gladly turn off the blocker to keep getting their YouTube fix. So we’re left with a tiny percentage of users who would actually be upset about this.