NFS do not use access control but IP address restriction.
You can add as many clients you need to any shared folder.
Synology do not recommend using subnets as this give any client connected to your network same permissions as yourself.
Enable and start services to make Manjaro act as a NFS client.
$ sudo systemctl enable --now nfs-client.target
$ sudo systemctl enable --now NetworkManager-wait-online.service
List the available mounts on your diskstation
$ showmount -e diskstation
❯ showmount -e diskstation
Export list for diskstation:
/volume1/data 192.168.x.x,192.168.x.y
/volume1/web 192.168.x.x,192.168.x.y
/volume1/video 192.168.x.x
/volume1/photo 192.168.x.x
/volume1/music 192.168.x.x
$ sudo mkdir -p /data/nfs/video /data/nfs/music /data/nfs/photo
Set permissions on the nfs sub folder structure
$ sudo chmod -R ugo+rwx /data/nfs
Note: Server name needs to be a valid hostname (not just IP address). Otherwise mounting of remote share will hang. - Arch wiki
Manually
$ sudo mount -t nfs diskstation:/volume1/video /data/nfs/video
If you want to auto mount shares on client add the share to /etc/fstab
diskstation:/volume1/video /data/nfs/video nfs auto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
You should have an idea on how you make your Manjaro connect to your NAS using NFS.