Harder to make work these days because backup.ab may become too large, or password-protected by recent double-digit Androids (which don't allow skipping encryption by pressing the greyed-out button either anymore).
"The UI for importing backup.ab is a little wonky" by/ever since its original alien author's admission in 2012.
However, a look at the Python source (comments) of the relevant plugin indicates that one doesn't have to try and import that entire (likely huge) archive for just a few lines from it:
The
https://github.com/nelenkov/android-backup-extractor prompts for the password, then turns the file retrieved over ADB into a more common, extractable format:
java -jar abe.jar unpack backup.ab backup.tar
The tiny map_data_storage.db or AmazonSecureStorage.xml from that archive should be digestible to the plugin as well, and contain all of the few lines it cares to import.
Calibre at least on Windows itself doesn't seem to have a way of importing .prc files straight from a tablet etc. (maybe due to the way it gets MTP-mounted) with (old enough) Kindle for Android, though on its Device menu it can list them.
However these do not need to be retrieved via ADB (nor then processed via ABE again):
Copying the files folder from Android/data/com.amazon.kindle to somewhere on e.g. C: will allow Calibre to "Add books from folders and sub-folders" in bulk when selecting the local copy of "files" and that "All e-book files in a folder are assumed to be the same book in different formats."