So as Kstars 3.6.0 no longer works below OSX 10.15 and I am not going to upgrade the hardware, I have re-purposed my old Mac mini (mid 2011, 5.1) into an Ubuntu machine.
The installation was easy, grabbed the Ubuntu iso (I picked the server one as I can't stand bloatware from the full desktop install) and burned it on a 4Gb USB stick.
Booted it (pressed the ALT key to access it) and ran the install. As I am not dual booting, I wiped the drive (I have other Mac machine at home...).
There was an error at the end of the install, it said: failed... but it wasn't too bad.
Booted in Ubuntu rescue, and reset the root password. From that point on after a reboot I carried on the setup....
Playing with i3 window tile manager (I used to run Awesome on Debian at work a few years ago).
Kstars 3.6.0 runs on Ubuntu 22.04 LTS on a Mac mini mid 2011.
The reason for this was because KStars 3.6.0 was released just before I went on vacation and there was an issue with my script so they just used the craft built version instead of the one built with my script. Apparently Craft is now being built with MacDeploymentTarget = 10.15. The reason they give in the comment is "As projects start to require c++17 we are now requiring 10.15" as shown here:
I also managed to fix my build script as well, so I rebuilt the dmg today and uploaded it. Please check to see that it works on 10.13 and 10.14 again. If not, then I should probably clean out my build directory and build again, but hopefully the issue is resolved.