I have a Bluetooth keyboard case for my Android tablet. All the time, I use Termux to ssh into my Linux machine over my home network and code on it in Neovim from my couch.
I don't bother with the default notes app on my phone. Termux + Neovim running vimwiki and syncing to a private GitHub repo is way better.
Most stuff you want at the CLI is in the Termux package repository. On the occasions when it isn't, you can install clang, make, cmake, ninja, whatever libraries you need, and build it from source. At that point most stuff just works.
Termux is incredible and single-handedly keeps me running Android.
But this is one of the things I really would love to have on my iPhone that I’m jealous of the Android ecosystem for. I know there are alternatives for iOS and I’ve used them (no need to list them here, this thread isn’t about iOS). For me, a really good terminal/CLI with good integration with the OS would be killer. But I know I’m niche and unlikely to see such a thing outside of SSHing to a remote VM.