NFS handles permissions based on the UID and GID of the user account accessing the share. (Assuming you haven’t restricted the share to a specific subnet or host IP).

When you create the NFS share, assign permissions using a group with a non-standard GID (doesn’t matter what, but pick something you’ll remember like 3000).

How you go about that will depend on the server you’re running the NFS share on. It’ll be different for Ubuntu or TrueNAS or Unraid etc - so read the documentation.

Once that is sorted, for each VM you need to create a group using that GID and assign the relevant users on each VM to be members of that group.

If you’re following best practices and running services as non-root, it’s usually also necessary to change the group ownership of the mount point directories on each VM so that the group you’ve just created with GIS 3000 (or whatever) is the owner.

edit: As a side note, because this tripped me up for a while - if you’re running LXC’s in proxmox, they’ll need to be privileged containers or you need to manually enable the NFS option for the LXC otherwise it doesn’t matter what you do with permissions, you won’t be able to mount the share.