1. Yes, the other submenus work properly.
2. InkCut is the only extension in Cutter/Plotter category.
3.
[root@banjah2002][/home/bane/.config/inkscape/extensions]# ls
inkcut inkcutext1.inx
I'll try to contact the author.
Thanks for help.
[root@banjah2002][/home/bane/.config/inkscape/extensions]# ls
inkcut inkcutext1.inx