From their Digital Rights Management page (link):
Effective January 20, 2026, verified purchasers can download the EPUB and PDF files of your confirmed DRM-free books.
Also lower in the same page:
Change DRM settings
You have full control over your DRM settings and can change them at any time. Your DRM setting affects future download availability for all customers, regardless of when they purchased your book. After you select not to apply DRM, any verified purchaser will be able to download EPUB and PDF files effective January 20, 2026. If you later apply DRM, no new downloads in EPUB or PDF format will be available. However, readers who already downloaded EPUB or PDF files will retain access to them.
And this applies to older releases too, as per the paragraph and steps immediately after.
And where to download the files, from the bottom of the page:
Reader download access
Effective January 20, 2026, readers can download EPUB and PDF files of your DRM-free books from their Manage Your Content and Devices page on Amazon. Only verified purchasers who have bought your book can access the EPUB/PDF files. Customers who borrowed your books through Kindle Unlimited or other services can't download the EPUB/PDF files, even if the books are DRM-free.
If readers downloaded EPUB/PDF files when your book was DRM-free, they will retain access to those downloaded EPUB/PDF files even if you later apply DRM. However, the option to download EPUB/PDF files will not be available after your DRM setting change is live (approx. 24-72 hours after you publish).
And lastly, found about it after finding a news piece on that (link of the news).
They're walking this back pretty fast. The fear they created in consumers of total lock-in must have had an impact on sales numbers.
Adjacent to that, concerns of preservation and right to ownership seem more and more mainstream, so I wonder if Amazon is also keeping tabs with it and making a strategical repositioning for when the cultural shift consolidates.