I'm just going to refer to this reddit thread, which is me explaining the situation and going through various troubleshooting, trying to set static ip, etc.

Basically everything was dandelions til internet borked (ISP side) and this shared residence (Tokyo) went out completely. I thought it was just me so I tried reseting everything, but now using WAN port is basically not possible although no signs or order of events suggest any sort of damage to the router itself.

https://www.reddit.com/r/HomeNetworking/comments/kbqkfo/help_no_internet_via_router_after_internet_went/