K. I was able to install on my kubuntu laptop a set of xcursor themes. I could see the files in /usr/share/icons though none of them had a xmc extension. Used the head command from a terminal I confirmed that the files had Xcur in their header, so I assume they are xcursor files. magick, convert, and gmic cannot open one of these files. But, GIMP CAN open them. I assume from that point I can save to whatever format I desire. I think you’ve gotten this far as well. I’ve never used GIMP in batch mode so I don’t know how to write a batch procedure (because scheme!) but perhaps this can help: GIMP - GIMP Batch Mode
I just discovered that converting xmc in batch comes with other challenges. Like defining the hotspot which is different for each file. I am using 24.04 and thought that Nautilus will support thumbnail preview for xmc files. Looks like that’s not the case.
I have been playing with it for a long time. So I kind of know it by heart.