fn key of other keyboard is not working

These days I bought The keyboard Mx key for mac.
but the key "Fn" of Mx keys is not working

[example]
(fn + ctrl + option) + a..z -> not working
fn + n -> not working
(ctrl+option+cmd) + any key -> working

It seem "fn" isn't triggering when it key down with other keys

as far as I know some Logitech keyboards only use the fn key internally on the keyboard hardware to modify functionality but don't actually send the key to the system

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