I cannot pass a parameter inside a function to another function (Python)

I successfully defined a parameter and passed it to a function but when I return to main menu that parameter's value is completely reset and I cannot use it anywhere. The value of the parameter stays only within the second function. Like, the parameter cannot communicate with the whole program as far as I understand.

def main_menu(subtotal):
  while True:
    print("1) Appetizers")
    print("2) Option 2")
    print("3) Option 3")
    print("4) Option 4")
    print("5) Option 5")
    print(" ")
    print("Current overall subtotal: $" + str(round(subtotal,2)))
 
    while True:
      try:
        choice = int(input("What is your choice? "))
        break
      except ValueError:
        print("Please enter whole numbers only.")


    while choice > 5 or choice < 1:
      print("Please choose an option from 1 to 5")
      try:
        choice = int(input("what is your choice? "))
      except ValueError:
        print("Please enter whole numbers only.")

    if choice == 1:
      appetizers(subtotal)
    """
    elif choice == 2:
      option_2(subtotal)
    elif choice == 3:
      option_3(subtotal)
    elif choice == 4:
      option_4(subtotal)
    elif choice == 5:
      end(subtotal)
      return subtotal
    """

def appetizers(subtotal):
  while True:
    print("1) Option 1")
    print("2) Option 2")
    print("3) Option 3")
    print("4) Return to Main Menu")
    print(" ")
    print("Current overall subtotal: $" + str(round(subtotal,2)))
   
    product_amount = 1

    while True:
      try:
        choice = int(input("What is your choice? "))
        break
      except ValueError:
        print("Please enter whole numbers only.")

    while choice > 4 or choice < 1:
      print("Please choose an option from 1 to 4")
      try:
        choice = int(input("what is your choice? "))
      except ValueError:
        print("Please enter whole numbers only.")

    if choice == 4:
      return subtotal
    else:
      while True:
        try:
          product_amount = int(input("How many would you like? "))
          break
        except ValueError:
          print("Please enter whole numbers only.")

    while product_amount > 100000 or product_amount < 1:
      print("Please choose an option from 1 to 100,000")
      product_amount = int(input("How many would you like? "))

    if choice == 1:
      subtotal = subtotal + (product_amount * 4.99)
    elif choice == 2:
      subtotal = subtotal + (product_amount * 2.99)
    elif choice == 3:
      subtotal = subtotal + (product_amount * 8.99)

For this project's sake, I don't want to use global variables. I only want to use the subtotal variable as a parameter throughout the program and continuously alter its value throughout the program and make calculations with it. I want to do this by passing it through other functions.