i dont undertand …. why menu columns without a sub menu item are not going to display on mobile ONLY on mobile ?

i am note sure to understand ….

sub menu 2.1 and sub menu 2.2 have no sub menu, but i just want to display sub menu 2.1 and sub menu 2.2 on mobile, when i click on menu 2….

is there a method to do this easily ? even if i must create 2 menu (mobile and desktop)