Cluster compatibility level has been introduced with:

Bug 1877675 - [RFE] Introduce Datacenter and cluster level 4.5

It tracks:

- Bug 1725166 - [RFE] Private VLAN / port isolation

- Support for Intel Icelake Server Family 

- Bug 1814565 - Report disk.usage for VMs with RHEL 8 guests

- Bug 1852718 - vGPU: VM failed to run with mdev_type instance

- Bug 1853194 - VM with disk on iscsi on environment with SELinux enforced fails to start on host - Exit message: Wake up from hibernation failed:internal error: child reported (status=125): unable to set security context

- Bug 1876605 - VM with scsi hostdev (scsi_generic custom property) fails on start:'node-name too long for qemu'

+Martin Perina , +Arik Hadas , +Tal Nisan , +Dominik Holler  feel free to add if I missed something.

I think that having a page on oVirt documentation with features and requirements per supported cluster compatibility level would help.

Gianluca, maybe you can open a bug for it?