The connection is made over the mysql protocol, and it is SQL, so you could migrate to mysql/mariadb if need arises.

RAFT is an algorithm and Akka is a "framework" ?

They are different layers of abstraction.

Storage and computing are two layers in a normal application. You are free to switch computing layers as long as storage layer speaking some standard protocol.

AKKA + AKKA persistent, how can you switch the computing layer?

Akka includes a facility for distributed data based on CRDTs, but I can't recall what it uses for consensus.