Only a rabbit experienced vet will be able to accurately treat it, but it most likely is a skin illness that has only grown and gotten worse due to past conditions. Whether it’s something that just needs moisturizing ointment or something that needs medication, an exotic rabbit vet will tell you. It’d also be highly beneficial to go so you can assess for other health issues.

Lucky bun! Thanks for giving him a home.

I agree, it could be any of those things really. If it’s just fur mite, I really recommend Revolution rather then Ivermectin injections. It just seems to be more effective. In many places, it’s prescription only, so a trip to the vet would be required.

There are some primary conditions where exfolative dermatitis may be a secondary condition, so you’d want to rule things like that out.
If a hormonal disorder is something you’re concerned about, the vet could do some bloodwork. You may wish to have blood work done regardless, if you are considering having him neutered. That will give some indication of how he will do under anaesthetic.