So CGNAT is exactly what it is. I tried using it through a VPN and it worked great. But through T-Mobile Home internet it doesn't work at all.

That IP you're using is being shared with bots and other malware to attack sites. So instead of trying to filter out all the potential attacks through things like fail2ban, etc. what archive.is is doing is to just block entire ip address ranges.

It makes me yearn even more for IPv6 now.