wow it took me 2 days of de-installing , configuring with started as a ZFS problem on OMV 6 with standard kernel and moving to the proxmox kernel where my docker and portainer was not working anymore.... then i finally run into this post. This should be pinned or something as its a very big issue is you decide to use the proxmox kernel i found out now i have apparmor and i removed it. But.... i don't know how i got it as i never installed OMV on top of debian, and recently upgraded the dist with OMV script to go to OMV 6
I wish i had found this post 2 days back, after removing apparmor, reboot and installing portainer through web-gui of OMV everything is working again as before.
TIP , please add also the OMV 6 tag to the post !!!