I just found another related issue:
Ubuntu doesn’t provide packages for the Caladea and Carlito fonts. These are metrically compatible fonts with Microsoft’s default fonts Cambria and Calibri and can therefore be used as direct substitutes without changing the layout/appearance of a document. With other words, they are needed to provide for compatibility with modern MS Office files (I believe starting with MS Office 2007 Cambria and Calibri have been the default fonts). LibreOffice will automatically substitute Cambria and Calibri with Caladea and Carlito as long as those fonts are available on the system.
Moreover, Caladea and Carlito are used as default fonts in the “modern”-template which is shipped by default with LibreOffice. Thus, this template is broken as well at the moment.
I think the proper solution to these font-related issues would be to make sure that all fonts packaged with LibreOffice by default (see link in my first post in this thread) are also available on Ubuntu. I would suggest to make this a goal for the Ubuntu 20.04 LTS release cycle.
Edit: I stand corrected. There are packages for Carlito and Caladea in Ubuntu’s universe repository but somehow LibreOffice can’t use them with the “modern”-template. Might be - again - a problem with the template itself or maybe the LibreOffice package doesn’t depend on those two fonts so that they are not pulled from the repository. Not sure where the root of the problem lies…