Tkinter checkbox returns wrong value in Python

So im currently writing a program to Watch a folder and sort out all Files and their extensions to new folders with the extension names. Right now i am trying to implement a settings Part, where a new Window from Tkinter open and you can check if you want to start the programm with windows on startup or not.

but im not able to receive the right checkbox value, is always say FALSE even if i checked the checkbox.

The whole Code is:

from tkinter import filedialog
from tkinter import *
from tkinter import messagebox
from pystray import MenuItem as item
import os
# main_with_ini.py
import configparser
import pystray
from PIL import Image, ImageDraw
import Handler as h
import threading
import getpass

filename = ""
configfile_name = "config.ini"
icon_name = "icon.png"
fenster = Tk()
folder_path = StringVar()
USER_NAME = getpass.getuser()
CHECKBOX_STATE = 0


# print('sys.argv[0] =', sys.argv[0])
# pathname = os.path.dirname(sys.argv[0])
# print('path =', pathname)
# print('full path =', os.path.abspath(pathname))

def add_to_startup(file_path=""):
    if file_path == "":
        file_path = os.path.dirname(os.path.realpath(__file__))
    bat_path = r'C:\Users\%s\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup' % USER_NAME
    with open(bat_path + '\\' + "open.bat", "w+") as bat_file:
        bat_file.write(r'start "" %s' % file_path)

def createConfig(configfile_name, section, key, value):
    global filename
    config = os.path.join(os.path.dirname(sys.argv[0]), configfile_name)

    write_config = configparser.ConfigParser()
    write_config.add_section(section)
    write_config.set(section, key, value)
    cfgfile = open(config, 'w')
    write_config.write(cfgfile)
    cfgfile.close()

# Check if there is already a configurtion file
def checkConfig(configfile_name):
    config = os.path.join(os.path.dirname(sys.argv[0]), configfile_name)
    # Create the configuration file as it doesn't exist yet
    if os.path.isfile(configfile_name):
        read_config = configparser.ConfigParser()
        read_config.read(config)
        watchPath = read_config['Folder_WatchPath']['PATH']
        folder_path.set(watchPath)
        return watchPath


    else:
        print('no config file yet')


# Systemtray
def quit_window(icon, item, window):
    icon.stop()
    window.destroy()


def show_window(icon, item, window):
    icon.stop()
    window.after(0, window.deiconify)


def setup(icon):
    icon.visible = True


def withdraw_window(window):
    window.withdraw()
    image = Image.open(os.path.join(os.path.dirname(sys.argv[0]), icon_name))
    menu = pystray.Menu(item('Show', lambda: show_window(icon, menu, window)),
                        item('Quit', lambda: quit_window(icon, menu, window)))

    icon = pystray.Icon("name", image, "FolderWatcher", menu)
    icon.run(setup)


def settings():
    settings = Tk()
    settings.title("Settings")

    info_text = Label(settings, text="Script Starten bei Windows Startup")
    info_text.grid(row=0, column=0, pady=20)

    boolvar = BooleanVar()
    boolvar.set(False)

    Checkbutton(settings, text="Autostart", variable=boolvar, command=lambda: callBackFunc(boolvar)).grid(row=0,
                                                                                                          sticky=W)
    btn_save_set = Button(settings, text='Save', command=lambda: saveSettings(settings, CHECKBOX_STATE))
    btn_save_set.grid(row=2, column=0)
    settings.mainloop()


def callBackFunc(checkbox):
    print("Oh. I'm clicked")
    var = checkbox.get()
    print(var)


def getBool(boolvar):  # get rid of the event argument
    print(boolvar.get())


def getAutostart(button):
    global CHECKBOX_STATE
    if button.get():
        print("checked = " + str(CHECKBOX_STATE))
        CHECKBOX_STATE = 1

    else:
        print("notchecked = " + str(CHECKBOX_STATE))
        CHECKBOX_STATE = 0


def saveSettings(window, checkbox):
    messagebox.showinfo(message="Einstellungen wurde gespeichert", title="Save")
    if checkbox:
        temp = "TRUE"
        createConfig(configfile_name, "SETTINGS", "AUTOSTART", temp)

    else:
        temp = "FALSE"
        createConfig(configfile_name, "SETTINGS", "AUTOSTART", temp)
    window.destroy()


def background(func, args):
    th = threading.Thread(target=func, args=args)
    th.daemon = True
    th.start()


def changePath():
    # Allow user to select a directory and store it in global var
    # called folder_path
    global filename
    global folder_path
    filename = filedialog.askdirectory()
    folder_path.set(filename)
    if len(filename) > 0:
        h.watchDir(filename)


def savePATH():
    global filename
    if len(filename) > 0:
        createConfig(configfile_name, "Folder_WatchPath", "PATH", filename)
        messagebox.showinfo(message="Der Ordner wurde gespeichert", title="Info")
    else:
        messagebox.showinfo(message="Bitte einen Order zum Beobachten auswählen", title="Info")


def action_get_info_dialog():
    m_text = "\
************************\n\
Autor: Minh Tuan Vuong \n\
Date: 27.05.2020\n\
Version: 1.00\n\
Email: Minhtv@web.de\n\
************************"
    messagebox.showinfo(message=m_text, title="Infos")


def minimize_win(window):
    Wm.iconify(window)


def on_closing(window):
    if messagebox.askokcancel("Quit", "Do you want to quit?"):
        window.destroy()


def main():
    fenster.title("Folder Watcher")

    info_text = Label(fenster, text="Suche den Ordner aus, denn du beobachten möchtest!")
    info_text.grid(row=0, column=0, pady=20)

    # Menüleiste erstellen
    menuleiste = Menu(fenster)

    lbl1 = Label(master=fenster, textvariable=folder_path)
    lbl1.grid(row=1, column=0)
    button2 = Button(text='Durchsuche', command=lambda: background(changePath, ()))
    button2.grid(row=2, column=0, pady=20)

    # Menü Datei und Help erstellen
    datei_menu = Menu(menuleiste, tearoff=0)
    help_menu = Menu(menuleiste, tearoff=0)

    # Beim Klick auf Datei oder auf Help sollen nun weitere Einträge erscheinen.
    # Diese werden also zu "datei_menu" und "help_menu" hinzugefügt
    datei_menu.add_command(label="Speichern", command=savePATH)
    datei_menu.add_command(label="Minimiere", command=lambda: withdraw_window(fenster))
    datei_menu.add_separator()  # Fügt eine Trennlinie hinzu
    datei_menu.add_command(label="Einstellungen", command=settings)
    datei_menu.add_separator()  # Fügt eine Trennlinie hinzu
    datei_menu.add_command(label="Exit", command=fenster.quit)

    help_menu.add_command(label="Info!", command=action_get_info_dialog)

    # Nun fügen wir die Menüs (Datei und Help) der Menüleiste als
    # "Drop-Down-Menü" hinzu
    menuleiste.add_cascade(label="Datei", menu=datei_menu)
    menuleiste.add_cascade(label="Help", menu=help_menu)

    # Die Menüleiste mit den Menüeinrägen noch dem Fenster übergeben und fertig.
    fenster.config(menu=menuleiste)

    fenster.protocol('WM_DELETE_WINDOW', lambda: on_closing(fenster))

    fenster.mainloop()


if __name__ == '__main__':
    filename = checkConfig(configfile_name)
    if filename:
        print("Watched Folder is " + filename)
        background(lambda: h.watchDir(filename), ())
    else:
        print("No Watched Folder defined yet")
    main()

The Problems lays in this methods i guess:

    def settings():
        settings = Tk()
        settings.title("Settings")

        info_text = Label(settings, text="Script Starten bei Windows Startup")
        info_text.grid(row=0, column=0, pady=20)

        boolvar = BooleanVar()
        boolvar.set(False)

        Checkbutton(settings, text="Autostart", variable=boolvar, command=lambda: callBackFunc(boolvar)).grid(row=0,
                                                                                                              sticky=W)
        btn_save_set = Button(settings, text='Save', command=lambda: saveSettings(settings, CHECKBOX_STATE))
        btn_save_set.grid(row=2, column=0)
        settings.mainloop()


    def callBackFunc(checkbox):
        print("Oh. I'm clicked")
        var = checkbox.get()
        print(var)

def main():
    fenster.title("Folder Watcher")

    info_text = Label(fenster, text="Suche den Ordner aus, denn du beobachten möchtest!")
    info_text.grid(row=0, column=0, pady=20)

    # Menüleiste erstellen
    menuleiste = Menu(fenster)

    lbl1 = Label(master=fenster, textvariable=folder_path)
    lbl1.grid(row=1, column=0)
    button2 = Button(text='Durchsuche', command=lambda: background(changePath, ()))
    button2.grid(row=2, column=0, pady=20)

    # Menü Datei und Help erstellen
    datei_menu = Menu(menuleiste, tearoff=0)
    help_menu = Menu(menuleiste, tearoff=0)

    # Beim Klick auf Datei oder auf Help sollen nun weitere Einträge erscheinen.
    # Diese werden also zu "datei_menu" und "help_menu" hinzugefügt
    datei_menu.add_command(label="Speichern", command=savePATH)
    datei_menu.add_command(label="Minimiere", command=lambda: withdraw_window(fenster))
    datei_menu.add_separator()  # Fügt eine Trennlinie hinzu
    datei_menu.add_command(label="Einstellungen", command=settings)
    datei_menu.add_separator()  # Fügt eine Trennlinie hinzu
    datei_menu.add_command(label="Exit", command=fenster.quit)

    help_menu.add_command(label="Info!", command=action_get_info_dialog)

    # Nun fügen wir die Menüs (Datei und Help) der Menüleiste als
    # "Drop-Down-Menü" hinzu
    menuleiste.add_cascade(label="Datei", menu=datei_menu)
    menuleiste.add_cascade(label="Help", menu=help_menu)

    # Die Menüleiste mit den Menüeinrägen noch dem Fenster übergeben und fertig.
    fenster.config(menu=menuleiste)

    fenster.protocol('WM_DELETE_WINDOW', lambda: on_closing(fenster))

    fenster.mainloop()


if __name__ == '__main__':
    filename = checkConfig(configfile_name)
    if filename:
        print("Watched Folder is " + filename)
        background(lambda: h.watchDir(filename), ())
    else:
        print("No Watched Folder defined yet")
    main()

If i encapsulate only the code for the checkbox windows without the main windows, the checkbox code is working.

from tkinter import *


def settings():
    settings = Tk()
    settings.title("Settings")

    info_text = Label(settings, text="Script Starten bei Windows Startup")
    info_text.grid(row=0, column=0, pady=20)

    boolvar = BooleanVar()
    boolvar.set(False)
    Checkbutton(settings, text="Autostart", variable=boolvar, command = lambda : callBackFunc(boolvar)).grid(row=0, sticky=W)
    btn_save_set = Button(settings, text='Save', command=lambda: saveSettings(settings, CHECKBOX_STATE))
    btn_save_set.grid(row=2, column=0)
    mainloop()

def callBackFunc(checkbox):
        print("Oh. I'm clicked")
        var = checkbox.get()
        print(var)

if __name__ == '__main__':
    settings()

But in the main program, it will not return the right value, only False