A lot of coed college cheer teams(even the really good ones!) will take boys with little-to-no experience if they have the strength to lift the flyers above their head. Especially with his gymnastics background, your son will hardly be denied a spot on most teams. Cheer is definitely worth it!
I would ask your DD why she mentioned starting cheer to you. Is it for the social aspect of seeing her friends? It might be a good idea to help her set up a virtual movie night or something similar with her friends. Like you said, if she doesn’t really want it, she could regret it.
If not, if...