You can open .xml files within Figurenotes software, which enables you to open files from Sibelius, MuseScore, and many more music programs. Please ensure that you only open files with a single part, as Figurenotes will try to put everything into one part, which will not work in stage 1, as it results in overlapping notes.
When exporting as an .xml in Sibelius make sure your project has a title otherwise when you open the unnamed .xml file in Figurenotes the programme will crash.
You can Save As MIDI to export the file in MIDI format, enabling you to open the file in other notation software, such as Sibelius, GarageBand, Logic, and many others. The part will open in conventional notation.
Please use the plugins to create Figurenotes Stage 3 notation.