Tiddlywiki used to be my favorite thing for keeping todo lists and notes about whatever I am working on. It has not aged gracefully though. There have been several issues as web browsers have tightened permissions surrounding file:// URIs. It works on mobile but its very clunky. I wrote a simple http back end for it but every time I request the file ornsave I am sending 1MB+ of data across the network. The author of Tiddlywiki is working on a next gen version but its still lacking some things I want too see like offline use via indexeddb.

All that being said I have been doing something similar to the OP but using Google Keep. It works offline, on mobile, or on the desktop.