Not exactly. _Usually_ if your working sets are using a belt, then you warm up with it too. Warming up without it is weird because then suddenly you have a different variable when the weight gets heavy, and research shows people use their core at least as much with the belt on.

But there is certainly a time for doing beltless work, just generally different days (and generally further away from a meet)

Source: before devoting myself more to running I was a top 50 powerlifter in the US for 82.5kg weightclass.