I agree with the programming part. I just started playing with GForth on Android, but I wonder if people know of other options. (IMHO something like Emacs or Factor would be ideal.)
What surprised me is the fact that Termux always ships the latest version of Nim. They're practically the first to update the compiler on new version release, even compared to rolling Linux distros, OpenSUSE Tumbleweed and Arch taking second and third place after a week or two.
I also have full blown Neovim IDE configured for Nim. In combination with a custom 7-row keyboard[1] it's even somewhat comfortable to use for a quarter of an hour =).
[0] - https://termux.dev/en/
One challenge is to evolve the terminal / text paradigm so that useful tinkering becomes possible/confortable on the smaller mobile devices. It doesn't help that these devices are being reduced to optimizing finger swipping ("software" keyboards etc.) and little else.
And of-course who knows where it would lead if it was actually a first class member of the OS...
There used to be a Clojure one with the challenges from Clojure, but no longer works in recent Android versions, and the server no longer exists (4Clojure).