Not able to boot on ZFS raid 1

[Veidit]

Good day

I have a Dell RX740xd with a PERC 330 mini card in IT-mode. It shows upp well and I can choose to install it as zfs raid1 during the Proxmox installation.
But after I boot UEFI lists both disks but says that it can't boot from them. What could I be doing wrong? I would prefer a raid controller in IT-mode and use zfs, but should I reflash it in raid-mode and use raid1 on the card instead?

Thanks in advance!

 

[bobmc]

Might only work in legacy / bios mode

 

[Veidit]

Might only work in legacy / bios mode

No, it didn't even show up in legacy / BIOS mode, I have tried.