In the Home assistant database (which is SQLite IIRC).

UI-generated configs are not stored in the database, they end up in a collection of JSON files in a .storage directory inside your config directory.

And there is no real API for you to interact with it. I would build my own config system if I could, but they don’t seem interested.

SQLite is highly automatable if you can deal with downtime to do your migrations.

I'm sure there are things they could do to better support the power-user engineer use case, but at the end of the day it's a self-hosted web app written in Python that has strong support for plugins. There should be very few things that an engineer couldn't figure out how to do between writing a plugin, tweaking source code, and just modifying files in place. And in the meantime I'm glad that it exists and apparently has enough traction to pay for itself.