I have installed nfs-kernel-server packages. I think it is possibly a permissions issue.
I briefly considered mounting it on the host (Proxmox) layer, but the way I have things set up, I only power on the NAS if I need to access it. Most of the time the Proxmox hardware will be booting up when the NAS is off and I think it will cause boot issues trying to mount a NAS share which it cannot find.
“noauto” sounds like a step in the right direction. I might give it a shot.
Many thanks. You’ve been very helpful.