Can't boot from installed os on nvme

Hey Community,

So I have a R640 with the 10x backplane that supports NVMes and all nvme needed cables are installed.

iDRAC regognices the nvme drives and lists them correctly in PCIeSSD BaySlot 2:1, PCIeSSD BaySlot 3:1  etc.

I booted an Ubuntu 22.04 LTS installation (Supported OS for R640) and installed the os without errors on one of the nvme drives. 

After rebooting it just shows "Unavailable: ubuntu". As far as I understand the R640 supports booting from nvme and I can't seem to work out why it doesn't want to boot from them. (Tried other os as well but ubuntu is officially supported to trying to get that working as a start). 

Secure boot is disabled, nvme is in non-raid mode (only mode available)

If anyone has any ideas what may be the problem please tell me :)

Zoey