May be I missed some hidden feature but…
It is very nice to be able to return to Hub after closing a project, but….
If I have the Audio Perf Monitor opened, there is no closing the hub, it disappears but the Audio perf Mon window stays open and we don’t quit Cubase.
A ‘Totaly Quit Cubase Button’ would be welcome 
The Cubase Quit button, in my opinion, is the close button of the Hub. The Hub is the parent window for all subsequent windows, including the project view and, of course, the performance monitor. Closing a parent window without its associated child window(s) can only be described as a bug.