Cannot connect to 19c with SQL Developer though database is mounted and opened, error ORA-01034
You have to restart your DB instances while listener's are up and don't restart the listener after that. When DB's are started: try to connect to them locally (just with username/password) and locally through tnsnames (username/password@tnsname) If listeners are shown correct status and you are able to connect locally with tnsnames: make sure the sam tnsnames file is on your client and there is no firewall between DB and client.