[TJG]

@niluje: I'm new to this thread (and message board back end); please bare with me.
For kicks I started researching the capabilities of an old Kindle (K4) due to its eInk screen and read somewhere it might be possible to use USB to... (long laundry list) so I tripped across this 8+ year old thread and spent the past so many hours reading the starting and a few of the ending pages worth of posts - long story short, thanks for 'that' level of dedication!

Regardless, I have an old K4 which I was going to tinker with but ran into a brick wall with KUAL. (JB was effortless, but I installed fonts, python and ss just in case there was a dependency from there - which doesn't seem to be the case.)

kindle-mkk-20141129-r18833.tar.gz/...k4-ALL went in without issue.
Copied KUAL-v2.7.28-gb9db5b3-20221001.tar.xz/KUAL-KDK-1.0.azw2 into /documents on the device and it crashed once opened. (Repeated everything and rebooted before opening KUAL - no difference.)

KUAL shows up in the top-left of the screen
A moment afterward:

Main class instantiation threw a Runtime Exception. Please contact the developer.

Log file:

[11/30/22 8:10 AM] KUAL (v. 2.7)
java.lang.RuntimeException: java.lang.NoClassDefFoundError: com.mobileread.ixtab.kindlelauncher.ui.UIAdapter
	at ixtab.jailbreak.SuicidalKindlet.<init>(Unknown Source)
	at ixtab.jailbreak.SuicidalKindlet.<init>(Unknown Source)
	at com.mobileread.ixtab.kindlelauncher.KualKindlet.<init>(KualKindlet.java:46)
	at com.amazon.kindle.kindlet.internal.kb.zdb(tpb:275)
	at com.amazon.kindle.kindlet.internal.kb.KU(tpb:439)
	at com.amazon.kindle.kindlet.internal.lifecycle.o.call(psb:412)
	at edu.emory.mathcs.backport.java.util.concurrent.FutureTask.run(fw:491)
	at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.IX(qr:959)
	at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(qr:803)
	at java.lang.Thread.run(Thread.java:989)
	at java.lang.Thread.startup(Thread.java:1066)
Caused by: java.lang.NoClassDefFoundError: com.mobileread.ixtab.kindlelauncher.ui.UIAdapter
	at java.lang.Class.runStaticInitializers(Compiled Method)(Class.java:1578)
	at com.mobileread.ixtab.kindlelauncher.KualKindlet.getUI(KualKindlet.java:269)
	at com.mobileread.ixtab.kindlelauncher.KualKindlet.<init>(KualKindlet.java:152)
	at ixtab.jailbreak.SuicidalKindlet.<init>(Unknown Source)
	at ixtab.jailbreak.SuicidalKindlet.<init>(Unknown Source)
	at com.mobileread.ixtab.kindlelauncher.KualKindlet.<init>(KualKindlet.java:46)
	at com.amazon.kindle.kindlet.internal.kb.zdb(tpb:275)
	at com.amazon.kindle.kindlet.internal.kb.KU(tpb:439)
	at com.amazon.kindle.kindlet.internal.lifecycle.o.call(psb:412)
	at edu.emory.mathcs.backport.java.util.concurrent.FutureTask.run(fw:491)
	at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.IX(qr:959)
	at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(qr:803)
	at java.lang.Thread.run(Thread.java:989)
	at java.lang.Thread.startup(Thread.java:1066)

Any thoughts would be appreciated!