This kind of thing gets posted every couple of months. Databases like Pinecone and Redis are more cost-effective and capable for their special use case, often dramatically so. In some circumstances the situation favours solving the problem in Postgres rather than adding a database. But that should be evaluated on a case-by-case basis. For example, if you run something at scale and have an ops team the penalty of adding a second database is much smaller.

(I run a medium-sized Postgres deployment and like it, but I don't feel like it's a cost-effective solution to every database problem.)