In a database with the option to export all notes or single notes as markdown.

If you haven’t tried Trilium in a while you should. It has improved significantly and has a nice clean new theme.

I’ve been using Trilium for years and the feature set has grown significantly. It is pretty simple up front but has all the bells and whistles just an extra click or two away. It is entirely free (no up sells, pro tiers, subscriptions, etc - you get it all free, so do support the developer if you can!) There is a third party android app that works quite well if you need that and the pwa is quite good too. I’m pretty sure you won’t be disappointed. it seemed like almost every time I thought trilium was missing a feature, I would find out that it actually has it (or something similar). The only thing I would say is that if you’re a flat file only person, then it isn’t for you - it stores the notes in a database -even though they can be easily exported in a directory format.

Trilium Next has 2fa, note encryption and oidc support AFAIK, so the authentication should not be a concern. Every instance retains its own copy of the data and syncs with the server (if you have one) backups are made daily in the back end iirc. Exporting the data is trivial too in both HTML and markdown.