PW3 5.12.3 Way to fix jailbreak manually when mntroot is working?

Hi,

I jailbroke my PW (2015) years ago.
Unfortunately it got multiple OTA Updates.
As I did not use it much I don't remember exactly if and what Hotfixes I've applied or how I made the jailbreak safe.
I have an entry in my list for KUAL, but I can't open it (could not be started... please retry).

I played around with it for a bit and found out, that using emergency.sh I can mount root rw and copy files to it. From my understanding this should be enough to get it into a working state.
I tried copying the keystore and the pem file to the correct location in hopes to be able to start KUAL but it didn't work.
I also tried to install it via bin files but I was either unable to select the update or the update failed.

I really tried to find a way to do this myself but couldn't and I didn't find something in the forum (maybe I wasn't searching for the correct phrases).

It would be nice if you could give me a hint on what I'm missing or an idea on how to go on.

Thanks in advance.