There is one limitation missing w.r.t multiattach feature of cinder volumes in following doc 

https://docs.redhat.com/en/documentation/red_hat_openstack_services_on_openshift/18.0/html-single/customizing_persistent_storage/index#proc_cinder-configuring-block-storage-volumes-that-can-be-attached-to-multiple-instances-at-the-same-time_customizing-cinder

Even though we can create bootable volumes with multi-attach enabled but customers cannot attach same bootable volume to multiple VM even with multiattach feature  as it remains unsupported

I would recommend to note added for the same in limitation section