I don’t recall where I read it, but I once read that a difference between pros and enthusiasts was that when pros go out, they tend to dress warmer than enthusiasts. I tend to follow that advice for cycling and running. A little warmer than I need to be… But I try to choose a layer that I can unzip if needed.
The other thing I’d mention is that if you have a good fan you might not get too sweaty on the trainer in the first place.