You should upgrade to Oracle Database 19c. It is the latest "long-term-support" release that will get patches for March 2023 or March 2026 (as paid option). Many customers are already upgrading to this release for this very reason.
If you go to any other interim release you will only get patches for a limited period.
Dude! already supplied the AIX install guide where you can verify the OS requirements.
Is there a direct upgrade from 18.104.22.168.7 to 19c or does it have to be upgrade to 12.2 first?