I was trying to see what works and what doesn't and here's what I came up with.
- NOOK for PC doesn't work anymore.
- NOOK Study starts to sign me in works!
- NOOK for Windows works for me.
- NOOK for Android works on some of my devices.
The Windows app downloads books and I can remove the DRM using Calibre,
BUT the key that the Calibre dialog retrieves no longer works. The NOOK Study key works, though, and even after the incomplete login, the instructions in the B&N readme from the Tools found the working key.
The Android thing appears to be related to the TLS 1.2 updates a while ago. Older devices don't work, newer ones do. Unfortunately, Android-x86, even the latest version, no longer works, so I had to use a legit Android phone. The Android app also uses the same key as NOOK Study and books can be retrieved from a rooted phone ("/data/data/bn.ereader/files/B&N Downloads/Books").
Edit: If you need a copy of NOOK Study,
this link still works.