When you try to open a docx file the MS store opens and offers you like three versions of Office 365, one of which is free (which eventually opens up the web version of them).
LibreOffice is on the store, but it’s also not free for some reason. Apache OpenOffice is free on there. Neither of them appear in the list of apps when you try and open a docx file, although it does show a few programs that appear to be very thinly reskinned versions of OpenOffice on there…