> my tmobile 5g modem has ipv4 but changes ip every single page load, it's wild

They're probably using CG-NAT, though IP changes that often is a bit aggressive.

> They're probably using CG-NAT, though IP changes that often is a bit aggressive.

TMobile uses IPv4 addys in DOD's address space. They do change unexpectedly often.

And yeah. Being DOD IPs, they're cgnat'd behind tmobile's public ASN.