Can't create file system on RAID drive

New here but I’ve done a search and not found the answer.
I’ve installed OMV6 on a Pi4 with 2 x 4TB drives.
MDADM creation of a RAID 1 set worked following the instructions in the sticky and everything synced.
I can see the RAID set in OMV RAID management, but I cant create a filesystem, when I go to select the dvice, I only see my individula drives /dev/sda and /dev/sdb, not the RAID set /dev/md127.

Have I missed a step?

Kind regards