A combination of @treetrum's Kindle bulk downloader, the DeDRM Tools plugin for Calibre, and the looming deadline of downloads being switched off on 26th February was just what I needed to strip the DRM from 325 ebooks. I followed this guide https://www.cloudwards.net/remove-drm-from-kindle-books/ but it was reasonably self-explanatory. Thanks to all involved for helping to liberate my library!
https://github.com/treetrum/amazon-kindle-bulk-downloader
https://github.com/apprenticeharper/DeDRM_tools