Our infinitely powerful editor.
Unfortunately my personal search for the same has left me with 2 conclusions:
Android is terrible for this. Most ergonomic way is to use Orgro or something as read only, and if read-only is not an option, then use an the full Emacs port for android (available on f-droid) which cones with its own input-related challenges.
Ultimately what is going to work is getting something like GPD Micro, a small machine with dedicated keyboard. Anything short of that is going to fail one way or another.
Emacs in termux is slightly better imo if you don't need graphics because unlike the port, the keyboard stays open at all times.
update for later generations: https://org-roam.discourse.group/t/import-of-obsidian-notes/609/3
it seems to be easy and seamless to use org-roam with md-roam, and use obsidian on mobile and emacs on your real computer. I might update this post with more details once I tried it.
I am in a similar boat. I decided to write my own app (learning android development so it's going slow).
I was using orgzly earlier but it doesn't fit in with org roam workflows.
Also check out logseq and its mobile app. I have heard you can make it work since it can use org mode files as the backend.