I have enabled Ribbon UI and it looks like ribbon ui build in nineties. There is no obvious way to revert the change.
I think you can restore the default from the main menu?
View -> Toolbar Layout -> Default
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!
https://blog.documentfoundation.org/blog/2016/12/21/the-docu...