The database is Postgres, and the schema is quite sensible. You can (and I have) write normal SQL queries in psql to modify the data.

It might not be as easy as rsync to transfer data out, but I would trust it way more than some of the folder based systems I've had with local apps that somehow get corrupted/modified between their database and the local filesystem. And I don't think ext4 is somehow magically more futureproof than Postgres. And if no-one else writes an export tool, and you feel unable to, your local friendly LLM will happily read the schema and write the SQL for you.