GL-AX1800 router cannot access internet, possible modem connection isuse?

Could you use this command to double-check:

swconfig dev switch0 show |grep port

port 1 is WAN, and it works when it gets a speed.

Alternatively, you can connect a PC cable to the WAN port. If a red “X” appears, the port is damaged.
image
If the issue is a physical failure, please contact support for a return.