You can check two projects on top of sqlite using paxos and implement reciprocal rank fusion (RRF) and distribution-based fusion score (DBSF) on top of sqlite with sqlite's FTS and sqlite-vec extensions.

Project zaxonlite: https://github.com/insanai/zaxonlite

Project sqlodin: https://github.com/insanai/sqlodin

Just you need to remember sqlite support single writer at a time so both needs to work with that limitation. PostgreSQL uses MVCC, so performance for concurrent writes from multiple clients might be better. Did not do benchmark against it so cannot say.

For what it's worth, DuckDB does. See: https://duckdb.org/docs/current/core_extensions/vss

There's a few, even an official extension called Vec1.