I can second the recommendations i've read here.

My approach to knowledge management has been super simple. Everything is in git, in a big directory structure i've organically grown over time. I have so many notes.. 7 to 8 thousands of them.

Keeping it in git has allowed me flexibility to use it how i see fit. Sometimes i'm in emacs/nevom. Most the time i'm in sublime text because I have workspaces per project/concept.

Finally, for mobile, I push them all to my own gitea instance. I rarely need access to my notes on mobile but it's been something i've been thinking about more.

If anyone has any recommendations on how to read a directory of text files on android, i'm all ears.