I like the idea of this. I also using organizational tooling to deal with ADHD. The big thing that's missing from this for me is being able to make sub lists. I get it though, there's beauty in the simplicity of what you built.

Here's what I'm doing. Org-mode on desktop, and Organice on my mobile. I have Organice sync to dropbox. On the desktop, I have a few tiny rclone scripts that I can call from emacs to sync to dropbox. It's probably more complex than it needs to be, but it works.