I should ask you Lubuntu maintainers: please build LibreOffice with vcl:kf5 instead vcl:qt5. Because LibreOffice's vcl:qt5 backend still buggy and unstable. Look at it:
I just tried to use Lubuntu 21.04 beta, opened LibreOffice Writer and I wanted increase a scale of the page. So you can see what I saw: wrong vertical rule, ugly page view, etc.
