knc1 can correct me, but I believe you can still jailbreak using the serial port. the so called "Open Kindle" or hardware jailbreak.
Here are the instructions, but be warned, this is advanced hackery, side effects may include, but are not limited to - permanent bricking, damaged components, house fires, forest fires, etc.
https://www.mobileread.com/forums/sh...d.php?t=267541