I'm confused why this isn't handled by:

(
  press[1].toUpperCase() !== event.key.toUpperCase() &&
  press[1] !== event.code
) ||

'?'.toUpperCase() === '?' // true

Should we also be comparing:

(
  press[1] !== event.key &&
  press[1].toUpperCase() !== event.key.toUpperCase() &&
  press[1] !== event.code
) ||

I might be missing something super obvious here but this case:

( press[1].toUpperCase() !== event.key.toUpperCase() && press[1] !== event.code ) ||

is correct, it's properly returning false. However because it returns false, we check the second value, and then third value, which:

KEYBINDING_MODIFIER_KEYS.find(mod => {
  return !press[0].includes(mod) && press[1] !== mod && getModifierState(event, mod)
})

returns Shift, which when we apply !"Shift" it returns false 😅