The client libraries are those artifacts:
Java admin client - Maven artifact org.keycloak:keycloak-admin-client
Java authorization client - Maven artifact org.keycloak:keycloak-authz-client
Java policy enforcer - Maven artifact org.keycloak:keycloak-policy-enforcer
Java common classes used by other client libraries above - Maven artifact org.keycloak:keycloak-client-common-synced
The client libraries are supported with the last supported Keycloak server version.
It is possible that client libraries may work even with the older releases of the Keycloak server, but it is not guaranteed and officially supported.
It may be needed to consult the javadoc of the client libraries like Java admin-client to see what endpoints and parameters are supported with which Keycloak server version.