Icons with .ico extension aren't displayed in the 'Applications' menu

Example: 'xonotic' project installs the icon /usr/local/share/pixmaps/xonotic.ico file:

$ file /usr/local/share/pixmaps/xonotic.ico
/usr/local/share/pixmaps/xonotic.ico: MS Windows icon resource - 9 icons, 64x64, 32 bits/pixel, 16x16, 32 bits/pixel

It is displayed in the menu with an unknown icon.

XFCE-4 is installed from ports.

FreeBSD 13.1 STABLE