For higher res with releases after April 22, I believe your only option is kfx from Kindle for Android or Kindle for PC.
For Kindle for Android, see this post:
https://www.mobileread.com/forums/sh...&postcount=787
Basically Method 4 with a slightly newer version of the Android app.
For the latest K4PC, see the most recently updated fork of noDRM's DeDRM.