Install libreoffice-gtk by entering the following commands in the terminal:
sudo apt update sudo apt install libreoffice-gtk
Description:
transitional package for LibreOffice gtk2 backend
This package used to contain the LibreOffice gtk2 backend. The package has been renamed to libreoffice-gtk2 to distinguish it from the gtk3 backend. You can safely remove this package.
Homepage: http://www.libreoffice.org
Version: 1:6.0.3-0ubuntu1
Section: universe/gnome