I have the latest stable release of KStars installed on my MacBook Pro (Catalina) but I never use the Drag-to-trash method to uninstall an app. Because this quick fix has a significant drawback - all the application’s service files will be left behind on your Mac. These files will continue to consume storage space while the app was removed.
To completely uninstall/reinstall KStars or other bloated application completely, you need to remove its executable file and all the service files stored in ~/Library and /Library folders (as mentioned by rlancaste).
Here is list of the most common folders that store KStars orphans: