I've reported a bug on the KDE bugtracker with kstars-bleeding (from the unstable PPA) on ubuntu 21.04, which happen as soon as you start the application.
I've provided a backtrace, but is the KDE bugtracker the prefered way to submit a Kstars bugs ? bugs.kde.org/show_bug.cgi?id=439811
I successfully built (locally using git clone) and ran kstars on both my laptop and desktop. Perhaps the kstars-bleeding package needs to be rebuilt for AMD64 21.04...