LibreOffice has several themes that makes it look like MS Office (e.g. ribbons, modern UI, etc).
Select TOOLS > OPTIONS > ADVANCED > Enable experimental Options (WARNING this is experimental and may be unstable) > OK and then RESTART LIBREOFFICE. On restart VIEW > TOOLBAR LAYOUT > NOTEBOOKBAR. You can then play with the options with VIEW > NOTEBOOKBAR > CONTEXTUAL GROUPS/ CONTEXTUAL SINGLE / TABBED.
It is actually View -> Toolbars -> Customize -> Notebookbar but within that there is only "Tabbed" option which doesn't really show a way to change themes.
This is a perfect example of actions that make adoption harder. This should have been at most 2 clicks and prominently displayed assuming LibreOffice wants to be a great alternative to MS Office and make the transition easier. I have been using Linux daily for over 20 years now and it is not intuitive to me - it doesn't make me very optimistic about the experience for a new user.
Found it - thanks! I wish this was more easily accessible to new users - it actually makes a difference in terms of organization of icons and ease of finding things.
Select TOOLS > OPTIONS > ADVANCED > Enable experimental Options (WARNING this is experimental and may be unstable) > OK and then RESTART LIBREOFFICE. On restart VIEW > TOOLBAR LAYOUT > NOTEBOOKBAR. You can then play with the options with VIEW > NOTEBOOKBAR > CONTEXTUAL GROUPS/ CONTEXTUAL SINGLE / TABBED.