I've installed Linux Mint v20.2 MATE on my Asus laptop (4GB RAM and 500GB HDD) and have tried to install KStars using the fo;;owing instructions :-
Linux Download: Install KStars from your Linux distribution software center. Under Ubuntu/Mint, you can install the latest KStars by typing the following commands in the console:

sudo apt-add-repository ppa:mutlaqja/ppa
sudo apt-get update
sudo apt-get install indi-full kstars-bleeding

I got "General Error" on running the first command.

Can anyone help, please?