Aren’t you worried about a single point of failure if you keep everything in 1 file?
yes. though i have a bunch of large files, one per project. but grep works on one file as easy as several, so i've started doing a week per file in a per-project directory.
I use markdown in an IDE (vscode). It’s very nice. You get: some formatting, auto indentation, indentation, identifier search (jump to heading with fuzzy search), code highlighting, etc.
I used to do this and it worked pretty well I thought.
I eventually broke it into years (YYYY-MM-DD-notes.txt and just grep'd the directory.
Finally I made it to markdown files also stored in the same directory.
It was great for searching.
By Karpathy: https://karpathy.bearblog.dev/the-append-and-review-note/