the T4 has its static IP adress
My question was whether you configured this 'static IP address' via OMV UI or not. If you did it the OMV way then Debian's ifupdown package controls the NIC but if you leave things as they are when booting first time (or set a static address via nmtui) then Network Manager has control (and with NM this should work -- I have no idea about ifupdown since I hate using anachronistic mechanisms from last century)