Not sure of the hardware specifics, but "ARM" is not saying anything significant. You have to see if the specific processor used has mainline support in the present or in a past kernel that you can use.

For instance, Android is a scheme where google takes a Linux kernel, strips absolutely everything they can out if it and documents thoroughly. All the thing can do is run the app environment, but the kernel is incomplete with no hardware support. All the manufacturer must do is add the hardware support modules at the last possible moment. This makes it possible for manufacturers to only add binary support modules. The entire arrangement is designed to exploit the end user with these orphaned kernels and hardware you can never own. The hardware is undocumented anywhere, and each device is different enough that reverse engineering one will do nothing for supporting the next.

I'm not saying your device has an orphaned kernel, but this is what to look for in any device. Mainline kernel support means full ownership. Proprietary is always theft of ownership.

So here is the jailbreak thread for the paperwhite, and here is the master list for other models.

There used to be Duokan, which was an OS-replacement. I can't for the life of me find an install image. If you do, let me know. I'd like to try it out.

And in my searching just now I've also come across fread-ink (project on hold since 2020), inkbox (mostly for Kobo devices, but some kindle support) and an old hackaday article about HOPE XII which I can't find any further information on.

Best of luck freeing your Kindle!

I remember "Jailbreaking" mine and getting shell access and some things, not sure if there's any like, custom ROMs that make it a better e-reader though. It's been a while.

I have jailbroken a couple of old e-ink kindles, and as far as I know, custom ROMs just straight don't exist any more. There have been a couple of attempts, some successful, but the device is so old they've pretty much fallen off the internet. The base OS is Linux, around a 2.6 kernel, and I'm fairly sure everything apart from the bootloader is just on relatively unprotected flash memory. Aside from the reader software it's a pretty standard Linux. To the point where one of mine actually runs an old Debian chroot.

I'm not near my PC now, but I'll link the jailbreak forums when I can. You'll need a fair bit of technical knowledge and judicious use of archive.org, the link rot is a very real problem.

Amazon hasn't used the "Kindle Fire" term for a while, They're now just "Amazon" Fire tablets; I would imagine for Simplicity so people don't get one thinking it's just an eInk eReader.

Kindle Fire was the original name of Amazons Android tablets. They later became just “Fire Tablets” and dropped Kindle from the name.

You’re seeing a lot about flashing the Kindle Fire because they still come without Google apps installed and some users believe that makes them very hamstrung. A custom ROM like LineageOS makes it a “real” Android tablet.

So, the Kindle OS is really basic.

If you’re able to jailbreak, look at installing KUAL and KOReader and that should change your experience enough to not need an entire new OS.