Yes, you can use the Zyxel NWA50AX access point with Swisscom's Internet-Box 3. The NWA50AX is a WiFi 6 access point compatible with WiFi 5/6 standards, which correspond to the technologies supported by the Internet-Box 3.

To connect it, plug it into the LAN port of the Internet-Box 3 (the NWA50AX has a Gigabit Ethernet port [properties]). No specific configuration is mentioned in the official Swisscom resources for external access points, but the generic settings for external routers include setting VLAN ID 10 and DHCP Option 60, although this mainly concerns routers used as a complete replacement.

In complementary access point mode, it should work without these advanced settings, but for optimal integration, consult the Zyxel documentation on AP mode. WiFi 6 compatibility is confirmed on both sides.

If in doubt about the specific configuration, the Swisscom community (10,000 users) can provide practical advice.