‘.m4r’ is the file extension name for an iTunes ringtone. It’s exactly the same as ‘.m4a’ (= ‘mpeg4’ audio file), but with the ‘a’ changed to ‘r’ to differentiate their purposes.
Audacity’s useful ‘Chain’ function offers the following six export formats:
However, Audacity’s File>Export Audio function seems to offer twelve or more export formats:
How can I add ‘Export to M4A’ to Audacity’s Chain function?