I was in Ronda in April (2018) with a small mobility scooter and did fine. The town has a few hills, but most of them are in the old town and aren’t generally steep. It can be a bit bumpy due to the cobblestones, but the new town has paving. We didn’t stay overnight so I don’t know if there was accessible accommodations, but I would think so as its quite a bit larger than it appears from photos.
I don’t know about public transportation as we’d rented a car and drove from Granada (also accessible).
Overall, Spain’s accessibility is some of the best I’ve seen in Europe. It appears they have made a concerted effort to make as many places accessible as possible. The Spain rail system (Renfe) has the Attendo service (there’s an app for that) and you can sign up for someone to meet you at the train and use the portable left to raise you up over the steps onto the train.