MySQL Shell 8.4.0
To use a MySQL instance as a Read Replica, it must meet the following criteria:
The instance must be a standalone MySQL server.
The instance must be MySQL 8.0.23, or higher.
The instance must not have any unmanaged replication channels configured.
The instance must use the same credentials as those used to manage the Cluster.
When an instance is added as a Read Replica, the AdminAPI runs
the same compatibility tests on it as it does an instance being
added to a Cluster. The same variables are checked, and so on.
As such, it is recommended you run
dba.checkInstanceConfiguration() or
dba.configureInstance() before attempting to
create a Read Replica.