A new jailbreaking tool, WinterBreak, was released earlier this year. It can jailbreak even the latest generation Kindles, as long as the device has not been updated to 5.18.x firmware. 5.18 firmware is available for 10th, 11th and 12th gen Kindles, and was released last month. OTA updates usually propagate over weeks or even months, so even if you have used your Kindle recently, there's a good chance the update hasn't reached your device.
Some older devices can be jailbroken with another tool. Only 1st generation Kindle, and Kindle Touch (4th gen) cannot be jailbroken.
Once jailbroken, you have freedom to do pretty much anything you want with the device. Get rid of the mostly useless Amazon interface, and replace it with KOReader. Or go crazy and install Linux.
You can get the tools and guides from this page: https://kindlemodding.org/jailbreaking/getting-started
And if you prefer to watch a video, this one shows how to jailbreak, why you might want to do so, and what new features you can get:
https://www.youtube.com/watch?v=Qtk7ERwlIAk
Genuine question, why jailbreak an ereader? Is it to install another OS?
As it is an Amazon device, someone might simply want to de-Amazon their Kindle. Perhaps because of the megacorporation that Amazon has become, or just to boycott USA.
The interface on Kindles isn't exactly the best out there. For one, it's very focused on selling you new books, while reading those books was almost a second thought for the designers. The settings to adjust the reading experience is limited. One font size might be too small, but the next bigger is too big. Margins and line spacing have very limited settings. Also, Kindles doesn't support EPUB, which is ridiculous considering it is the most common e-book file format - we are talking about an e-book reader device here.
You can install Linux if you want to, but it probably isn't very useful. There are also games and some other apps. You can also repurpose the device, if you don't want to use it for reading. For example, if you are using Home Assistant, you could turn your Kindle into an information display or control panel.
thanks for the response. that makes a lot of sense.