Also on OS3 file recognition is done through Def_Icons, thanks to the def_ icon you can associate icon and tool, without Def_icon you will not be able to associate anything, see OS 3.0/3.1, which do not have def_Icons "by default", and therefore can never these two OS recognize a file, except executables (associated hammer), text files and some other singular format.
Unfortunately Scalos is a system that does not work well on AROS, to associate a Def_Icon you must use "ScalosFileType," and this tool unfortunately does not work on AROS..