Staying on CentOS 8.4 is not responsible patching policy.
- CentOS does not have extended update support for minor versions like RHEL does. You will not get security and other fixes.
- CentOS Linux 8 ends at the end of 2021, the future is Stream. (Red Hat didn't have the courage to cut over to Stream prior to 8, long story.) Updates will stop and you will not see 8.6.
Decide if you wish to use CentOS Stream or some other RHEL build.
Switching from CentOS 8 to 8 Stream is a matter of swapping the release repos and dnf distro-sync
Or, switch to Alma, Rocky, RHEL, or Oracle EL with the tools they recommend.
Get the latest version into an usable state, whatever that means. You might be testing applications, repackaging or rebuilding software, or filing issues so other people can help with getting it working on updated RHEL.
I deferred avoided talking about recovering your CentOS 8.4 because it is an option that will take some work. Anaconda installer will not downgrade the existing install for you. Attempt dnf history rollback
to revert to prior to the big update. Unfortunately, that may be a difficult transaction to complete. You may wish to reinstall new copy of the OS on the desired version and restore data. And review all the updates you are deferring. Come up with a plan to mitigate what they fix in some other way, such as building your own packages, or doing other security controls.