ok so there is a known issue with the 5.9 kernel and nvidia driver. you have to roll back to the 5.8 kernel.
You can do this in the OMV extras "Kernel" tab. Change it to 5.8 and reboot. you should also hit the button "hold current kernel" that you don't update it the next time.
Thank you 1000000 times for letting me know this page exists. The amount of times my server has rebooted to a newer kernel and my Nvidia runtime containers didn't start until I reinstalled the driver........