I recently had to rebuild by drive, reinstall macOS 10.15.6 on my 2015 MacBook Pro, and restore my apps from Time Machine.
When I try to launch SkySafari Pro 6, it first shows a banner saying that it's verifying.
Then it pops up a window to verify my Apple ID.
Then it goes into a loop saying that it is verifying. Never actually starts.
I uninstalled the app using CleanMyMacX and downloaded the app from the Apple App Store.
It goes through the same process, never actually starting up.
I have no problem with Starry Night Pro Plus 8 other than I haven't gotten my head around using it.
I have a second drive that I can boot up from that contains macOS 11 (beta), and SkySafari Pro 6 works fine there. And I have a 2014 Mac Mini running macOS 10.15.6 where SkySafari is working just fine.