It sounds so simple - but in this specific case a bit of doc reading is required as upgrading the RMAN catalog to handle Oracle 18.104.22.168 databases is not as trivial as in the past.
Thanks to a German customer and a friendly colleague from Sales Consulting in Stuttgart I have learned my RMAN lesson for Oracle Database 22.214.171.124 this week. A simple "upgrade catalog" is not the correct step once you'd like to handle backups of Oracle 126.96.36.199 databases in your current catalog schema.
Even though you may not have ever heard before about Virtual Private Catalogs you need to follow this guideline:
The doc tells you to run this step first:
Please ignore the "-all" option printed in the doc - this is a known docu bug
If you miss this step the upgrade of the catalog will fail with a warning that your user lacks privileges
$ rman CATALOG my_catalog_owner@catdb recovery catalog database Password: RMAN> UPGRADE CATALOG; RMAN> EXIT;
It should work now
Referances link: https://blogs.oracle.com/UPGRADE/entry/rman_catalog_upgrade_to_oracle