"Where is outline mode?"
The bug's still open: https://bugs.freedesktop.org/show_bug.cgi?id=38262
Grandfathered in from: https://issues.apache.org/ooo/show_bug.cgi?id=3959
It seems crazy to me that such a common usage mode doesn't seem to be driving any development work.
I'm one of a large number of people who won't be using LibreOffice until that RFE's addressed properly (nope, Navigator view is not an equivalent thing).