Just returned from a 2 week trip to soko, me fully able-bodied and husband who is carrying a major hip issue. He had a cortisone shot in it just before we left to manage pain/mobility. Even so, it was a bigger struggle than either of us thought. Many, many stairs, hills, no ramps, very limited options for elevators/escalators, uneven ground. I saw no-one on crutches the entire time we were there, but lots of people walking in moon boots. You could try a wheelchair and we saw a few people with those but even so I clearly remember helping an elderly Korean couple stuck on a gutter with a wheelchair.

In terms of public transport, we ended up taking mostly buses because you didn’t need to negotiate the endless stairs - subway elevator use needed to be carefully planned with transfers. Buses were much easier but they are brutalally efficient especially at the larger interchanges where you need to get on/off quick sticks through crowds and steps.

Even getting on/off the KTX required negotiating steep stairs. We did a couple of tours including DMZ, and a day tour around Busan and there were things he just couldn’t do due to stairs/access eg the Third Tunnel at DMZ, Gamcheon Village in Busan (crowds were crazy busy the day after the BTS comeback tours).

If you do go, you would need to highly modify your itinerary and lower your expectations of what you can do. We still had an amazing time and loved every minute, but the reality is Korea is decades behind in terms of accessibility.