On a file share, a notes directory with each category as a subdirectory, and plain text files for each note. Accessible from my computers and phone.

On my laptop, the launcher for my text editor (Pluma) points to a bash script that creates a blank text file YYYYMMDD_text in ~/.drafts and opens that file with Pluma. If it already exists, YYYYMMDD_text_1, or whatever increment is created. That's mostly to take advantage of Pluma's autosave feature, which only works with already saved documents. Then I save the document to the file share if it's worth keeping.