There's an apparent workaround for mounting shared volumes into Unprivileged LXCs though it was a real pain for me (a noob) to figure it out. I used the forum post below to feel my way through it. You might also just try using a Privileged LXC if the security concerns don't bother you.
It's probable that I'm missing something but I couldn't get the share to be available to any other VM or LXC on ProxMox until I passed the pool from TrueNAS back to ProxMox.
I'm all for getting rid of the TrueNAS VM as long as I can reassemble the zfspool in ProxMox without losing the data (though if I did, no big deal). And I'd also like a user friendly way of monitoring the health of my disks.
There's an apparent workaround for mounting shared volumes into Unprivileged LXCs though it was a real pain for me (a noob) to figure it out. I used the forum post below to feel my way through it. You might also just try using a Privileged LXC if the security concerns don't bother you.
https://youtu.be/aEzo_u6SJsk
https://forum.proxmox.com/threads/tutorial-unprivileged-lxcs-mount-cifs-shares.101795/