NoSQL databases are not a magic solution for CAP, they just make different trade-offs, so nothing stops you from using a RDBMS and choosing your own trade-offs

NoSQL databases are not a magic solution for CAP, they just make different trade-offs, so nothing stops you from using a RDBMS and choosing your own trade-offs too. For instance, you could choose to lose the C and have a multi-master PostgreSQL cluster by taking some measures, like using uuids and appending-only. In practice, you always have to solve some things on the application layer (e.g., distributed queries), so that's why out-of-the-box solutions are popular.