I believe Ant Financial has published an open source one but iirc the English language documentation is sparse.
It uses IVFFlat indexing, but could be extended to support product quantization / ScaNN.
I googled and did not find much pertaining to "ant financial" and "postgres". Perhaps your google-fu is better than mine...
It’s not a relational db, but it supports Graph-like connections between objects, which makes it really easy to model your relations.
I believe Ant Financial has published an open source one but iirc the English language documentation is sparse.