I tried various GUI text editors on Android, but they tend to be buggy or hard to navigate. Then there's the fact that I can just open a tmux session, detach, ssh into my phone and attach it.
Do you have the keyboard split in landscape? As soon as I go landscape in termux I can't see the terminal. Also I've tried vim on mobile and have to commend you for doing it more than once lol.
Hacker's Keyboard is a good Android keyboard for doing terminal stuff. It adds a lot of the keys you need to efficiently work in terminal. Only Android keyboard worth using.