same here, SYNOLOGY 6.2.4, NFSv4 shared enable (also tried with NFSv3)
from LAN, Proxmox 6.3.6 => webUI, add NFS : OK
from WAN (port forwarding enable, firewall OK):
- Proxmox 5.4 => webUI, add NFS : OK
- Proxmox 6.3.6 => webUI, storage -> add NFS => wait and spin, and nothing
my workaround...