Weirdly, one was Facebook. The reason for all the other failures was that almost every site had either changed their password requirements and reset everyone's passwords when I was locked up (and so far in the past for me that I had missed the boat and now was terminally locked out), or they had introduced some sort of multi-factor authentication, and again I had missed the boat on the change-over and re-authentication and could no longer get in.
Frustratingly the worst ones were the biggest accounts, e.g. Google, because most of these companies were now boasting that they had rid themselves completely of human support and that if you could no longer access your account then you should simply create a new one. Years or decades of stored data be damned.