My setup shouldn't have any red flags in it. I access the Internet using Comcast from the US, no VPN; the phone number I gave is a vanilla Verizon number (and tried another one as well); I have tried various browsers, even new installations just to see if things work if I remove all ad blockers and other extensions. Console Log in Devtools has a few errors but none seem like a smoking gun.

So what can a humble Internet user do in this Kafkaesque situation?