Speaking of, Vim is actually quite easy to set up on Android. Simply download Termux from F-Droid (the version of Termux on Google Play is severely out of date) and pkg install vim (or nvim if you prefer). (Also, full aarch64 linux terminal on non-rooted Android, woo!) Using Vim with an onscreen keyboard is agonizing, of course, but it does work (Termux provides the Ctrl and Esc keys). The F-Droid app Unexpected Keyboard is a recommended addition -- it's an alternative on-screen keyboard with no predictive text and swiping to the corners of each key for alternate symbols. It makes using Vim on a touchscreen at least moderately less painful.