LibreOffice probably still remains the most complete set of features and a pure open source option, but I can see why the free SoftMaker FreeOffice is also given a lot of credit: It opens very quickly, has a pretty slick more modern user interface, it has excellent MS Office compatibility, and it already has usable mobile apps for both Android and iOS (apart from Windows, macOS and Linux too).
So yes, on all of these fronts, LibreOffice does lag a bit. But LibreOffice is open source, and all advanced features are completely free. FreeOffice also does not open or edit existing PDFs.
See https://www.xda-developers.com/best-microsoft-office-alternatives/