gina@Mint-Desktop ~ $ sudo apt-get install indi-full kstars-bleeding
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package kstars-bleeding is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Unable to locate package indi-full
E: Package 'kstars-bleeding' has no installation candidate
gina@Mint-Desktop ~ $
These commands worked fine :-
sudo apt-add-repository ppa:mutlaqja/ppa
sudo apt-get update
We're looking for a file such as "mutlaqja-ubuntu-ppa-focal.list" which would have the following contents:
deb-src http://ppa.launchpad.net/mutlaqja/ppa/ubuntu focal main
deb http://ppa.launchpad.net/mutlaqja/ppa/ubuntu focal main
# deb-src http://ppa.launchpad.net/mutlaqja/ppa/ubuntu focal main
(These are for Ubuntu Focal, hence the keyword focal in my examples, it might be replaced with another release name if you're running a different release).
That's true. The two only solutions are to rebuild kstars from source on Xenial, or upgrade the system to the next long-term support with "sudo do-release-upgrade".