This issue often occurs in a Oracle database 12c&onward installation or restore operation. The error stated that multitenant container database not set up properly, which means we have to set the enable_pluggable_database to True while on restore steps.
To fix this, connect to your Oracle Database using the sysdba user:
sqlplus / as sysdba
startup nomount
Change the value of the enable_pluggable_database system parameter by typing:
ALTER SYSTEM SET “enable_pluggable_database”= TRUE SCOPE = SPFILE;
COMMIT;
Now, restart your db, now you can mount the database:
shutdown immediate
startup mount or startup