You can’t do it in any straightforward manner.
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If your keyboard uses QMK, there’s a patch to allow for Apple’s fn key in keymaps. It’s a bit shady, but you can read more about it here;
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If you’re not in qmk, you can use software on the map to remap a key to perform as fn/globe. If you do it natively, you’re limited to remapping other modifiers (see this)
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If you want to go a bit deeper on the software route, you can use Karabiner Elements to map any key to behave as fn/globe (or any other key you may want to).
The third one is probably the way to go if you don’t intend to use your keyboard in any other device than your Mac.