It was not obvious as the main menu was hidden. There is a button (top-right corner) to show main menu.
Re:LibreOffice 6.0 released
by mksaunders on Wednesday January 31, 2018 @08:09AM
(#16273521)
This is why it's still an exerimental feature, and the more testing and feedback the design community gets, the better!
View -> Toolbar Layout -> Default