Jellyfin on proxmox

[GrumpyNick]

What does your fstab file look like, can you share it?

Also these are incorrect, well two of them are:
{ echo 'mp0: /mnt/truenas/Movies/,mp=/mnt/Truenas' ; } | tee -a /etc/pve/lxc/104.conf
{ echo 'mp0: /mnt/truenas/Music/,mp=/mnt/truenas' ; } | tee -a /etc/pve/lxc/LXC_ID.conf
{ echo 'mp0: /mnt/truenas/Shows/,mp=/mnt/truenas' ; } | tee -a /etc/pve/lxc/LXC_ID.conf

You need to increment the device each time like so:
{ echo 'mp0: /mnt/truenas/Movies/,mp=/mnt/Truenas' ; } | tee -a /etc/pve/lxc/104.conf
{ echo 'mp1: /mnt/truenas/Music/,mp=/mnt/truenas' ; } | tee -a /etc/pve/lxc/LXC_ID.conf
{ echo 'mp2: /mnt/truenas/Shows/,mp=/mnt/truenas' ; } | tee -a /etc/pve/lxc/LXC_ID.conf

Usually if the user and/or group is incorrect with an SMB/CIFS location it's down to what's in fstab.