The (often labeled as model 5G21 or FASTMILE 5G GATEWAY-3 ) is a high-performance indoor 5G receiver. It is designed for Fixed Wireless Access (FWA). Unlike a smartphone, this device is meant to replace a cable or fiber modem.
You cannot fully disable the NAT. However, you can enable "DMZ" to your own router. For most home users, just use the Nokia as a modem and plug your Asus/TP-Link into the 2.5GbE port. nokia fastmile 5g gateway 31 unlock