Launch the function using the "$Button" node or using a key on the keyboard in GODOT

In the scene, select $Button and find its Shortcut property in the inspector. Create a new Shortcut resource by clicking in the field, open the event array and add a new array element to it by clicking on Array[InputEvent] (size 0).

Now, when the $Button button appears, you can either click on it or press Enter key to launch the function (for example: start_game()).