It depends on what you call the "main tab", my 4.3.1 version of the app starts with the "start menu style" tab selected. The "basic settings" tab has the shutdown button options, yes you have to scroll down.
I am new to windows 10 and classic shell has been invaluable.
I think the tab that opens initially is the one last used.
The tab that contains the shutdown command option is titled Main Menu.
Anyway, thanks for the help.