I've written about the "world of postgres wire compatible" [0] and yes there are some databases that implement the protocol and don't implement postgres (see: immudb and ravendb) I give databases like CockroachDB more credit for actually making their intention and generally following through with implementing Postgres. Also unlike some others on my list CockroachDB really is meant as an OLTP replacement. Performance characteristics and operations will definitely differ but as solely a user/application developer you shouldn't notice as much.
[0] https://datastation.multiprocess.io/blog/2022-02-08-the-worl...