Determining which Operating Systems are supported for use with MTV can be a bit of a frustration and in some times incorrect: 

Currently the MTV Documentation  states the pre-requiste for migrating a source VM is :

"The VM operating system must be certified and supported for use as a guest operating system with OpenShift Virtualization."

This directs you to:
https://access.redhat.com/articles/4234591

This is a list of Operating systems that could run on Openshift Virtualization, if you should do a fresh installation.  This is not necessarily a list of Operating systems that can successfully be migrated using virt-v2v

That list is here: https://access.redhat.com/articles/1351473
Note that MTV's virt-v2v uses the RHEL8/RHEL9 host columns 

As an example we see Microsoft Windows Server 2012 R2 supported on 4.12 and 4.13 in the chart , yet 2012 isn't supported by virt-v2v on RHEL8/9.  So the MTV docs saying that the only prereq is that it is on the supported list isn't 100% correct.

We don't have a definitive matrix of supported and tested operating systems that can be successfully migrated and this would be helpful for customers and for support to be able to reference.