just bought a AX73 a few days ago, tried to replace my old asus RT-AC1200G+

ISP: M1
fibre modem: huawei HG8240H -- this is a very old modem.

now everything looks fine, but just don't have internet. once connect to asus's old router, internet back.

per

https://www.tp-link.com/sg/support/faq/3837/

the connection type is dynamic IP.

and I want to "wire the TP-Link router to ISP directly without another router in between like Pic 2"

I already tried the method in Pic 1, that works as well. however, I want the method in Pic 2.

the problem may due to the modem is too old, don't know if there is a solution or workaround for it ?