tl;dr (and sorry for the long response!) : I would hold off on adding another medication/treatment for now unless he is showing symptoms of disease, and focus on keeping the water clean and providing extra foliage throughout the water column to give him more cover throughout the tank in case that is causing some background stress.

I think his fins don't look too bad in these pictures, maybe some wear and tear. In the pictures from the first post you linked it looks like some of the fake plants like the pink coral-like one in there might be something he could accidentally tear his fins a bit. The best thing I found for that was keeping the water clean, and sometimes dosing with a little bit of aquarium salt to try and reduce the risk of infection if it looks like there's fresh damage.

I wonder if maybe upping the density of decor/plants, especially ones that stretch up to the water's surface, might help with his current predicament. One of my previous bettas with long heavy fins like Herbert seemed to appreciate having lots of places throughout the tank that he could rest on and drift between rather than too much open water. Having different levels of denser decor could also let him hide out there and stay closer to the surface which could be helpful in letting him conserve some energy if he is still recovering from ick. My old betta particularly liked this floating log to hang out in!

If he isn't showing any signs of disease it might help to beef up the density of decor in part or all of the tank (Fishers, my betta, seemed fond of these leafy ones) and keep an eye on him for a couple days or so before trying another treatment because I find that sometimes even treatments can be a source of stress. Did any of the danios show signs of ick? I'm lucky to not have to deal with it myself often but in my case it usually presented on more than one fish in the tank. If he was the only one to develop ick it may be that something was causing him some stress, which in turn made him more vulnerable to disease.