The easy way to fix that, is to show hidden files & go to "/home/your_user_name/.kde/share/config", while in normal login mode.

Edit the "kdesurc " file & change it from "super-user-command=sudo" to "super-user-command=su", save the file change. You should be able to, manage as per normal now.

This is NOT a new fix, this was used on 5.11 as well.

I wanted to go into MANAGE SOFTWARE PACKAGE,and i was asked for my password. I entered the password,and i received the message "CONVERSATION WITH SUDO FAILED.