I've successfully changed my screensavers on my Kindle Paperwhite 12th gen or PW6 (5.17.1.0.4). Wasn't my work, the following is the source of the hack that I used for it. It's in Russian:
https://github.com/madebyKir/ScreenSaverManager
https://4pda.to/forum/index.php?show...entry136521168
Attached is my translated version of it. I've used it on my own Kindle. I am not madebyKir, or affiliated with madebyKir.