I have the same issue and just now found it was because of Private Relay. I did not connect the fact that I had no issues accessing archive.is when I had a VPN on - which disables Private Relay. Since they got a location, not my location but a location they were hunky dory....

I saw this post and tried it with and without Private Relay and sure enough, turning it on is the issue. Good to know....

Edit: I updated Private Relay to "Maintain general location" for IP Address Location Settings and archive.is loads fine.

Second Edit: Maybe not, it all works now and I think it is either session or cache. I got to play around with it