Program freezing in python customtkinter

Question

i'm trying to learn tkinter/customtkinter so i followed a guide that made a youtube video downloader with customtkinter GUI but when i download a video the program freezes for like 10mins then it actually downloads

import tkinter
import customtkinter
from pytube import YouTube


def startdownload():
    try:
        ytLink = link.get()
        ytObject = YouTube(ytLink, on_progress_callback=on_progress)
        video = ytObject.streams.get_lowest_resolution()
        
        title.configure(text=ytObject.title)

        video.download()
        finishlabel.configure(text="Downloaded")
    except:
        finishlabel.configure(text="Invlaid")


def on_progress(stream, chunk, bytes_remaning):
    total_size = stream.filesize
    bytes_downloaded = total_size - bytes_remaning
    percentage_of_compeletion = bytes_downloaded / total_size * 100
    per = str(int(percentage_of_compeletion))
    number.configure(text=per + "%")
    number.update()

    bar.set(float(percentage_of_compeletion) / 100)


    


customtkinter.set_appearance_mode("dark")
customtkinter.set_default_color_theme("blue")

app = customtkinter.CTk()
app.geometry("720x480")
app.title("Youtube Downloader")

title = customtkinter.CTkLabel(app, text="Enter Video Link")
title.pack(padx=10, pady=10)

url_var = tkinter.StringVar()
link = customtkinter.CTkEntry(app, width=350, height=40, textvariable=url_var)
link.pack()

finishlabel = customtkinter.CTkLabel(app, text="")
finishlabel.pack()

number = customtkinter.CTkLabel(app, text="0%")
number.pack()

bar = customtkinter.CTkProgressBar(app, width=400)
bar.set(0)
bar.pack(padx=10, pady=10)

download = customtkinter.CTkButton(app, width=200, text="Download", command=startdownload)
download.pack(padx=10, pady=10)

#app run loop
app.mainloop()

tried asking chatgpt but that didnt help