I'm running unRAID v6.2.4 and trying to mount a share via NFSv4 from a linux client but it doesn't seem to be enabled/supported.
# mount -t nfs4 nas:/mnt/disk1 /mnt/disk1
mount.nfs4: Protocol not supported
# rpcinfo -s nas
program version(s) netid(s) service owner
100000 2,3,4 local,udp,tcp portmapper superuser
100024 1 tcp,udp status 32
100003 3 udp,tcp