First problem - only LibreOffice 7.0 and newer works on macOS 11 Big Sur. Nobody knows why. So if you use older version you should update your LibreOffice to 7.0.3
Second problem - if you have a Retina screen (HiDPI), then you can't use LibreOffice, because all text will be blured. There is a bug 138122
So, Apple, thank you!