I do agree with the author and others that I also wouldn't feel comfortable storing personal notes on Github. As I mentioned in a previous comment - you can use "git" without Github by hosting an instance of the open-source Gitea service.
My concern with this approach would be I've read through Directus' codebase and can understand it. With a self-hosted Git server like this I'd be worried if shit hit the fan and corrupted my Git files or stopped being maintained I'd be a duck out of water
And if you really just want a simple hosting system, https://tangled.sh is really easy to set up. It uses atproto (network underlying bluesky) as their identity provider and for tracking issues, PRs, comments, etc. Their "knot server" is basically just a little self-hosted go node that manages git repos. The project is fairly small atm and it's pretty much all in go so it's not too hard to skim through if you want to see how it works under the hood (or if you are afraid of needing to be able to keep it maintained long term).
Though I'd say, if you're going through all of the effort to self host something, git or otherwise, doing the "wrapper" is probably worthwhile anyway due to the convenience if you ever do need those features. It's not that much harder to do that than host a vanilla git server.
You should have the same concern with anything you're hosting yourself, and you should have 3-2-1 backups to mitigate that concern. Gitea just uses regular Git repositories under the hood last i checked, and Git is an extremely mature system; I'd expect 20+ year old repositories to work fine as long as the data are kept physically intact.