ISP or router seems to block .zip domains. I can only get access opening Tor, a VPN, or connecting from my phone on cellular or hotspot. I tried setting up custom DNS and even DoH but it didn't work. Since federation is a thing I can still access from other instances but the images are all blanked or errored. Unless I'm on an instance that caches the icons and Post images.
I think my workplace does block them because I remember recommending to them that they do because of their abuse potential (financialstatement.zip), I don't know if they still do though, I just know I recommended it and they said it was a good idea.