Well, this path seems to be the most appropriate for what I am for.

And more to that, both mergerfs and snapraid are available out of the box in the latest stable Debian release.

Thanks for pointing me at it!

To my knowledge not really much is available. You may use an intent to trigger database export and then use SQLite to scrape data.

Also keep in mind that data is kept in device specific tables.

https://codeberg.org/Freeyourgadget/Gadgetbridge/wiki/Intent-API

Gadgetbridge allows automatic SQLite database export to the location you specify.

Navigate to Settings -> Automations -> Auto export database, and from there you can configure the details.

You can put it into a shared Syncthing folder, or something alike, or process it with Termux + Tasker. Personally, I hesitate to send megabytes of data over the wire every couple of minutes, so I rigged up a script that extracts the required metrics (for now its my steps only, the rest does not seem to be accurate) and sends a payload to my queue, where a consumer script later adds it to the DB.

FTR: currently experimenting with scraping Gadgetbridge data into Grafana.