It came out over and over that there is no element in list, even though it was inserted in the list by using '.append'

I have fixed some coding parts over and over to solve a problem. The problem is that there isn't any element in order_list included in def new4(), even though the elements were inserted in order_list included in def new3() by using '.append' worked by checking checkbuttons, while running this program. So, the shell showed me an error. Can you help me? I can't make any progress...

from tkinter import *

global order_list                  
order_list = []

def new4():

    from tkinter import ttk
    root = Tk()
    root.title("window name")
    root.geometry("1300x700")
    
    dict={}

    strs = StringVar(root)
    lbl = Label(root,text="basket")
    lbl.place(x=400, y=30)

    def click():
        cl = strs.get()
        lbl4.configure(text="chosen goods: "+cl)

    lbl1 = Label(root, text="kind of the goods", font="NanumGothic 10")
    lbl1.place(x=100, y=70)
        
    Combx1 = ttk.Combobox(root, textvariable=strs, width=20)
    Combx1['value'] = (order_list[0:len(order_list)])
    Combx1.current(0)
    Combx1.place(x=700, y=70)

    btn1 = Button(root, text="review of the result",command=click,width=6,height=1)
    btn1.place(x=100, y=310)

    btn2 = Button(root, text="finish",command=quit,width=6,height=1)
    btn2.place(x=400, y=310)

    lbl4 = Label(root, text="choice result", font="NanumGothic 11")
    lbl4.place(x=400, y=390)
    print(type(strs))
    
    root.mainloop()
    



def new3():

    new3=Toplevel(window)

    new3.title("choosing goods")
    
    new3.geometry("1100x750+200+20")

    intro = "please select the goods (mutiple choices available)"
    label = Label(new3, text= intro, font=(100))
    label.place(x=400, y=10)

    global var01
    global var02
    
    var01 = IntVar()
    var02 = IntVar()
    
    Ch_A = Checkbutton(new3, text="eggplant   customer type: salad mania ", font=(50), variable = var01)
    Ch_A.place(x=100, y=170)

    Ch_B = Checkbutton(new3, text="potato   customer type: vegen", font=(50), variable = var02)
    Ch_B.place(x=100, y=250)
    
    button = Button(new3, text = "next", font=(100), command = new4 )  
    button.place(x=1000, y=570)
    if var01.get() == 1:
        order_list.append("eggplant")
    if var02.get() == 1:
        order_list.append("potato")

window = Tk()

window.geometry("700x500+400+100")

button01 = Button(window, text='start', font=100, fg='blue', command=new3)

button01.place(x=200, y=400)

window.mainloop()