I have two physical Oyster cards ("new" cards, that is with a "D" on the reverse side.) We used them on our last trip. I have been unable to create an Oyster Card account (for one card) on my USA New Jersey desktop or Ipad. It appears that the TfL website (needed even to "activate" the IOS App [TfL Oyster]) defends against non-UK sign-ins.
I used my September London hotel address for the App's demand for a UK address and it was accepted. But I don't have any control over my IP address, of course! I have tried entering the confirmation URL on Firefox, Edge, and Safari. All get the same TfL Error page. Thank you.