Its 126 Million (minecraft) vs 150 Million (roblox) users at the moment. Though it seems roblox outgrew minecraft just this year, for obvious reasons. They were competing for a longer time now, but so far minecraft had the upper hand.

I guess minecraft is more popular with older people who grew up with it and there is some limit reached which slows down minecrafts success at the moment. It seems minecraft was also rather silent in the last year. Animal Crossing and now Among Us are the hottest games everywhere, but aroung minecraft it was rather silent, even though it should have been more succesful with people staying at home the whole time, giving people more reason to do stuff in Minecraft.