technically it should not be a problem. the cloud is just a server at oracle and not at your location. how? well, how would you do it at your location? probably with create pluggable database command right?
Oracle expects you would choose Enterprise Edition – High Performance, because it "has" multitenant.. but I doubt, they have multiple versions of the installer. It's the same as Enterprise Edition, just costs more and you "get" the features.
Oracle just will not be happy if you would do it. But on the DB System you can install 19c GI too, upgrade whatever they provide, patch it as usual etc, you have ssh access to the system and can become root, you are the master of the VM in simple terms.