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
thanks for the response. that makes a lot of sense.