> LibreOffice’s UI is extremely dated imo

It feels so bland and hard to read. Maybe that's because of java. How did Excel 5.0 look so good?

There is no Java in core LibreOffice, it just has some weird Java-based extension system because of its Sun history.

LibreOffice uses an extremely dated, also messy, homegrown UI toolkit and has resisted the idea of switching to something last (really) updated this millennium (sic).