Problems with authorising ADE 4.5 and moving books to my ereader

I have ADE installed. It worked fine for years on my old XP computer, with an anonymous authorisation.

This year on my newer Windows 10 computer I had to install a newer version (4.5) with an online Adobe account.

That version will only let me read the books in ADE, and won't let me move them to my e-book library in Calibre or to my e-reader.

So I thought I'd done something wrong and got another standalone authorisation. So I followed the instruction on the Anonymous Activation page https://blogs.adobe.com/ebooks/2015/04/09/adobe-digital-editions-anonymous-activation/ and made a brand-new Adobe account online today (the one I'm posting from here), and tried first to re-authorise, then to uninstall and re-install ADE 4.5.11. but nothing worked - I can still read the books only in ADE on my computer screen. Uninstalling it left the existing library, which I hoped meant that I could still read those books after re-authorising on the new account.

But ADE keeps saying it's already authorised, shows me a long um:uuic number when I look at the details. It won't let me add a second authorisation.

If I try to de-authorise it, it wants the login for my first account. That email address and password work to login online at Adobe, but when I use it to try to unauthorise the newly-installed ADE 4.5 it says: can't remove the authorisation, try again later. It's been saying that for hours.

Calibre needs to be told where to look for the .der file authorisation key to let me load and read my new books, and searching for .der in Explorer doesn't net me any relevant results.

How do I get my new laptop properly authorised, with a .der file where it's needed, so I can read my books and manage my E-library the way I want to?