Followed all these steps from another thread
1) Login to OMV2) Choose "Plugins"
3) Find and highlight "OpenMediaVault CUPS"
4) Click install
5) Wait
That got CUPs installed, but printer drivers were still missing.
The Brother website was not useful, as they only supply x86 drivers, Arm...So I had to :
6) apt-get install csh
7) Manually find & install (via dpkg) brother-lpr-drivers-common
Manually find & install (via dpkg) brother-cups-wrapper-common
9) Manually find & install (via dpkg) brother-lpr-drivers-extra
10) Manually find & install (via dpkg) brother-cups-wrapper-extra
So that's CUPs with the relevant drivers, but still no installed printer...
11) Then navigate to openmediavault:631/admin
12) Click "Find New Printers" --- Did not find any printers