All books released after April 2025 have hardened drm. There are 2 options:
1. Have a Kindle that doesn't receive updates anymore. E.g. Oasis 3, or even older Kindles like the Kindle 4 Touch / Kindle 4 non-touch.
2. Only the latest firmware has the hardened DRM. You can have a newer Kindle that doesn't have the latest update, install jailbreak and use the ota renamer plugin to prevent updates.
3.
Use this process, if you run a x86 PC.