As the nova-cert package is updated in 11, you could see it when upgrade to 11, but not when upgrade to 12 as it is removed in 12.
Also it is not available on fresh OSP13 deployment, but will be shown in service list on 13, if we FFU from 10 to 13.
To delete the nova-cert service, I have followed what is mentioned in kbase article .
Could you try  if you have the environment available to check whether it is removing the entry or not ?
IIRC when I did testing locally, I could remove the entry with the proposed changes, or it might be true, that there could be two nova-cert entries, where only one is removed.
Created attachment 1696794 [details]
Created attachment 1696795 [details]
Created attachment 1696796 [details]
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (Red Hat OpenStack Platform 13.0 director bug fix advisory), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.