It lists VPN, Proxy, Tor, etc. Presumably a minus sign in a circle means you don't have the thing?

Freaky. They have a page explaining the concept (https://ipinfo.io/data/residential-proxy); when I checked it, there was a FOUC showing a full-screen, stretched image of what I think was Dario Amodei's face.

Neat. I almost said "surely this will only detect if your internet connection is itself being routed through a residential proxy", and then I realised that's effectively the same thing!

AFAIU that tells you if your access to ipinfo.io is thru a residential proxy, not if somebody else is using a residential proxy on your network.