My router cant get internet from old modem

i have an old modem, it has internet, when i connect that modem to my router, my router cant get internet, but all other modems is fine, just this one
where can be issue?

screenshot of old modem details:

by default the subnet would overlap.

change the openwrt LAN subnet, but you'll be double NATing.


i think i changed already, its like below:

you did indeed, how are the two devices inter connected ?