The upgrade process from RHEL 7.9 to THEL8.6, is a collection of other task (verification, preparation, etc) that involve different software, the principal is the leapp suite.
Now, if you mean an upgrade with a single cdrom that process all steps, i think that's not possible.
The official guide about the upgrade process, require a repository access.
Please check the official guide in the section "Red Hat Enteprise Linux 8/documentation/upgrading_from_rhel_7_to_rhel_8"
Here you could find all steps necessary for the upgrade.