I would guess not millions. All the relevant numbers are confidential, but estimates seem to suggest that having a million subscribers[0] is probably the level at which you could comfortably make it a full-time job, and there are maybe roughly 20,000 YouTubers with that many subscribers[1].
Bear in mind, YouTube is a global platform, so that number has to be spread across multiple countries. Therefore, other than maybe the US, I'd expect that no country has more than 1000 people whose job is full-time YouTuber. Also, for comparison, Lego has about 20,000 employees worldwide.[2]
[0] https://contentcareer.com/blog/average-salary-of-a-youtuber-...
[1] https://medium.datadriveninvestor.com/how-many-youtube-chann...
[2] https://www.statista.com/statistics/292314/number-of-employe...