"It's also possible to do it on top of other DBs like Postgres, but takes more effort."

Shameless plug: plpgsql_bm25: BM25 search implemented in PL/pgSQL (The Unlicense / PUBLIC DOMAIN)

https://github.com/jankovicsandras/plpgsql_bm25

There's an example Postgres_hybrid_search_RRF.ipynb in the repo which shows hybrid search with Reciprocal Rank Fusion ( plpgsql_bm25 + pgvector ).