Some scripts are disabled in the Makefile
Some scripts are disabled in the Makefile, namely xdg-su, xdg-copy, xdg-file-dialog and xdg-terminal: https://gitlab.freedesktop.org/xdg/xdg-utils/blob/master/scripts/Makefile.in#L24
I am using xdg-su and am forced to install it manually. The script itself works for me and I could not find any documentation why it is disabled. In openSUSE, a patch is maintained to enable xdg-su and xdg-terminal since 2014: https://build.opensuse.org/package/view_file/openSUSE:Factory/xdg-utils/install-some-more-scripts.diff
Please enable those scripts if there is no important reason to disable them.