Character code with shift or without

In my game you can set custom keys to controll the player.

Set the key “SHIFT + 6” to jump. Shift+6 in german QUERTZ-Keyboard is “&”.

Important: key “6” with or without shift should also execute jump.

When you press now a key

scene.input.keyboard.on('keydown', (event: KeyboardEvent) => {
  // ... jump

the event.key has on Shift+6 the value “&”. The &-sign is stored in the settings.
So far so good.

But, now you press only “6”.
How should the program know that 6 should be handled the same as Shift+6 / “&”?

I can not expect, that a user set all combinations of 6 in the settings.

event.keyCode is deprecated, so i don’t want to use it.

Somebody know a solution, how a shift or “non”-shift value could be converted in the useres keyboard locale?

(I know that onkeydown event.shiftKey is set, but that is not my question and it is not the solution for my problem)

Or is it not possible within the browser? I saw Keyboard-Api is still in development and works only in Chrome.