Following along from https://kindlemodding.org/jailbreaking/ I have a "Kindle Paperwhite (10th Generation)" aka PW4. It's running 5.17.1.0.3 Installing the jailbreak involved copying and overwriting a bunch of files. After the jailbreak, I was installing the "hotfix". This rebooted the device. After installing the hotfix, I had to open the "Run hotfix" book. This rebooted the device. After doing the MRPI and KUAL install and typing `;log mrpi` I did have an "application error" modal that showed up. After all that, it works! KOReader launches and I can still buy books from kindle / use it as normal.