Don't they offer older DRM schemes for older devices? Surely you do not have to update your kindle (especially if it is older) to read newly published books?
Yes, and you can for now still get AZW3 files (that can be unDRMed) through Download for USB transfer if you have a registered Kindle even if it's new enough to handle their new KFX format.
What is broken is that you can't use Kindle for PC/Mac to get AZW3 copies of books published on or after Jan. 3rd 2023 as it only lets you download with the latest version. As someone without a Kindle (and I'm certainly not buying one now) any new Kindle books would be locked down.
You can still break the DRM on books with Adobe DRM (like that used by Google Play books) or Kobo (they have their own DRM but also offer Adobe versions).
How's that "not possible to unDRM" thing works? The reader able to decipher the content to show it on screen means that everything it needs to decipher content is inside the reader, and can be extracted.