OME 4 on Openstack

I know this isn't supported officially, however our platform has no alternate virtualisation options so looking for some pointers and fully understand they're not guarantees.

I've tried booting an instance using only:
--property hw_firmware_type=uefi
--property hw_disk_bus=sata

I've also tried a whole other host of options, all of and on and everything in between:

--os_distro=opensuse
--os_hidden=false
--os_secure_boot=required
--os_version=15.40

--hw_machine_type=q35

We get no errors, but either it fails to boot, or it advises it's waiting for graphics - and I've left it in that state for over 24 hours.

We've given 72 CPUs and 64GB of memory to ensure it's got enough with no result. It can't possibly be this complicated, I must be missing something obvious.

Can anybody confirm what metadata / options they used in order to get a booting OME 4 in Openstack please?

Many many thanks in advance.