At the moment, if you are running High Sierra on an old mac then the highest Kstars you can run is 3.5.9 as 3.6.0 is no longer compatible.
Just downgraded back to 3.5.9

This was because it was built with craft. Please see this post: indilib.org/forum/general/12065-kstars-b...cbook-too.html#85538

Please test to see if it is fixed now.

I just rebuilt kstars dmg with fixes for the find dialog bug and the startup bug with asteroids.dat. The new dmg is now on the kde download site. Unfortunately, I did finally have to go along with KDE/Craft's decision to switch our support from 10.13 to 10.15 as the minimum MacOS level. Too many of the craft packages come from the binary server and were compiled for 10.15 now that they made the change. Having to rebuild everything for 10.13 and hope that it all builds without issue is problematic especially since they said that the reason they switched to 10.15 is because some newer versions of packages will no longer build properly for that version of MacOS. So sadly we will have to switch and I guess update our statement on the website that it supports 10.13 since it won't anymore