1. To mount with “NFS client” manually
sudo mount -t nfs4 -o defaults,_netdev [fs-XXXXXXXX].efs.[REGION].amazonaws.com:/ /path/to/mount/dir

2. To mount with “NFS client” automatically

[fs-XXXXXXXX].efs.[REGION].amazonaws.com:/ /path/to/mount/dir nfs4 defaults,_netdev 0 0
[Ubuntu20.04] EFS Mount