Open Office =/= Libre Office

The latter is a long standing fork of the former and considered the "FLOSS standard office suite". It has a "modern" ribbon UI, but you have to set it like that, it usually comes with the "old layout" by default.

OnlyOffice is another office suite which brings a ribbon UI by default.

While not open source Softmaker Office mimics Microsoft Office the closest (and claims the best available MS file format compatibility, but I cannot say anything about that).