Agreed, in Multi-tenant, where the user/customer owns the data, I always reach for SQLite first. Each user/customer gets their own SQLite DB. Then you have a common PG/SQLite DB for any common metadata, billing, etc.

That way when a customer leaves or they want a backup copy of their data, it's a rm <customer>.sqlite3 or .backup away.

Sometimes you can't do that for various (almost always non-technical) reason(s), but it's always my 1st choice.