Implement a pre-check (https://github.com/oamg/convert2rhel/blob/main/convert2rhel/checks.py#L36) which identifies that the centos is not updated to the most recent versions of the packages and doesn't use the latest version of kernel.

Why:

Because the not updated system has more chances to fail during the conversion, i.e. old kernel, old packages etc.

Hints to the solution:

KERNEL CHECK

1. Check the latest kernel version:
   [root@c2r-20210224190434 ~]# dnf repoquery kernel-core
   kernel-core-0:4.18.0-240.15.1.el8_3.x86_64
2. [root@c2r-20210224190434 ~]# uname -r
   4.18.0-240.15.1.el8_3.x86_64

These blue and red values should match, otherwise the conversion should be inhibited, because the system is not updated (what is required by our policy of the utility usage)

OTHER  PACKAGES:

[root@c2r-20210224190434 ~]# dnf update
Last metadata expiration check: 0:00:24 ago on Fri 09 Apr 2021 07:39:47 AM UTC.
Dependencies resolved.
Nothing to do.
Complete!

So basically check that dnf update stdout  contains Nothing to do. Or your solution