I read that one can modify the function that the close button of an Tk-Rootwindow uses. So I tried to implement one of my own but obvsly it's crashing. And I don't quite understand why. It seems to don't like the approach of me creating a toplevel popup and to parse the instance of the rootwindow into it. This is the error I get:

 File "C:\Users\marti\Documents\GitHub\Kniffel_GUI\game_window.py", line 77, in make_game_window
    rootwindow4.protocol("WM_DELETE_WINDOW", on_close(rootwindow4))
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\marti\AppData\Local\Python\pythoncore-3.14-64\Lib\tkinter\__init__.py", line 2400, in wm_protocol
    return self.tk.call(
           ~~~~~~~~~~~~^
        'wm', 'protocol', self._w, name, command)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_tkinter.TclError: bad window path name ".!toplevel"

I tried to use a global instance of the rootwindow and assign 'None' to it, but this is not working, I hoped that in runtime the program would be filled with the real instance but nope. So I kind of need to take the rootwindow-Object as an attribute for the function. This is my code:

def make_game_window():
    rootwindow4 = tk.Toplevel()

    #rootwindow4.iconbitmap('./assets/Dice_Icon.ico')
    rootwindow4.title("Best Kniffel")
    rootwindow4.geometry("420x600")
    rootwindow4.resizable(False, False)
    rootwindow4.protocol("WM_DELETE_WINDOW", on_close(rootwindow4))

....

def on_close(root):
    close_popup = tk.Toplevel()
    close_popup.title("SCHLIEßEN")
    close_popup.geometry("400x150")
    close_popup.resizable(False, False)
    close_popup.configure(bg="black")

    button_yes = tk.Button(
        close_popup,
        bg="red",
        text="Schließen",
        font=("Arial", 15),
        )
    button_yes.place(x=75, y=50)
    button_yes.bind("", root.destroy())

    '''button_no = tk.Button(
        close_popup,
        bg="green",
        text="Weiterspielen",
        font=("Arial", 15),
        command=close_popup.withdraw()
    )
    button_no.place(x=200, y=50)'''

Thank you for your help in advance, I know it seems like a weird way of trying to solve this problem. I felt like it all the time while writing this game but somehow it works, so my approach couldn't be so bad. But now I don't know how to deal with this.