Appreciate if someone can explain what is wrong with my coding

Hello Everybodies.
I am a noobie with python. I don´t have any background in coding and i just learned python from some python youtube course. But i am interested in python coding. I´m greatfull if someone can help me with my issue

My goal is to create an application with pysimplegui. With this application i can browse to my desired folder and it will display contents within a listbox so i can pick and choose what to do with it. But right now i don´t get that result. I´m testing my code with the left hand side of listbox.

This is my code.

import os
import PySimpleGUI as pg

Step 1: Set Theme

pg.theme(“default1”)

Step 2: Create Layout

ml_folder_column = [
[
pg.Text(“ML Crown Folder”),
pg.In(size=(30, 1), enable_events=True, key="-ML FOLDER-"),
pg.FolderBrowse()

],
[
    pg.Listbox(
        values=[],
        enable_events=True,
        size=(50, 20),
        key="-ML_FILE_LIST-",
    )
],
[
    pg.Button("Process", size=(7, 2)), pg.Button("Refresh", size=(7, 2))
]

]
ftb_folder_column = [
[
pg.Text(“FTB Folder”),
pg.In(size=(30, 1), enable_events=True, key="-FTB FOLDER-"),
pg.FolderBrowse()
],
[
pg.Listbox(
values=,
enable_events=True,
size=(50, 20),
key="-FTB_FILE_LIST-",
)
]
]

layout = [
[pg.Column(ml_folder_column),
pg.VSeparator(),
pg.vtop(pg.Column(ftb_folder_column))]
]

Step 3: Create Window

window = pg.Window(“ZIRCONIA CROWN APPLICATION”, layout)

Step 4: Event Loop

folder_location = “”

while True:
event, values = window.read()

if event == pg.WIN_CLOSED or event == "Exit":
    break

elif event == "-ML Folder-":
    folder_location = values["-ML FOLDER-"]
    try:
        files = os.walk(folder_location)
    except ValueError:
        files = []

    file_names = [
        file for file in files
        if os.path.isfile(os.path.join(folder_location, file)) and file.lower().endswith((".JPEG", ".xlsx", "docs"))
    ]
    window["-ML_FILE_LIST-"].update(file_names)

Thanks if i can get some helps.