Followed these instructions:
Create folder
Add to "exports"-file...
sudo nano /etc/exports
... a statement that allows NFS-connections to folder
/nfs/postgres 192.168.68.0/24(rw,sync,no_subtree_check,no_root_squash)
Restart NFS server
sudo systemctl restart nfs-server
Create volume in Docker / Portainer
Use NFS volume
TRUE
Address
192.168.68.118
Mount point
:/nfs/whisper