I don't even know how it's possible. However when I launch US2 through steam mind you, it still says I need steam running to open Universe Sandbox 2. After that it simply gives me the option to close out of it. Huh? Help would be appreciated. This has been occurring ever since I got the 20.6 update.
EDIT: This is no longer an issue US2 was updated to 20.7 so it now works again