Before configuring the truenas console, create the directory and change the owner to nobody:nobody. (To prevent privilege elevation risks, it's safest for NFS to treat the NFS connection user as "nobody."
sudo mkdir /mnt/nas/Share/nfs sudo chown -R nobody:nobody /mnt/nas/Share/nfs
Follow the instructions at https://www.truenas.com/docs/core/sharing/nfs/nfsshare/ (I could reproduce them here, but Truenas's will always be more up to date than what I can do - all I can do is add advice around it!)
NOTE: On the client you may need to install nfs-common and then you just mount it!
sudo apt install nfs-common sudo mount 192.168.1.9:/mnt/nas/Share /mnt/