Can you check if the unit is updated to the newest firmware? I suspect it is not. After updating please try again...

@BILJ Standard backhaul method is via WiFi, AND I do believe the Ethernet ports are available for devices to use. So by default I think that just adding another WiFi 7 (for more compatibility/ease)...

@Curtis11 Can you look on the bottom of the Deco and verify the Version number? And then check whether you have an appropriate firmware for it?

@JerrySmall Deco's can be accessed through a web browser, but the functionality is very limited, even less than the app. If you want the most flexible, probably ASUS brand has the most...

@DennisRatcliffe X55 V3? Which country please?

@RolfeJr If you set up the same SSID and Password then they should (hopefully) automatically connect...