Your code has a major issue: the while thread_request_token.is_alive(): pass line creates a blocking loop that freezes the GUI until the thread finishes. This is not ideal, as it prevents Tkinter from updating the interface properly. Instead, you should use a callback function once the thread completes.

Here’s a better version of your code using threading and Tkinter's after() method, which allows the UI to remain responsive:

import threading

def change_login_to_wait():
    frame_waiting.grid(row=0, column=0, padx=10, pady=10)
    frame_discord_login.grid_forget()

def change_wait_to_session():
    frame_discord_session.grid(row=0, column=0, padx=10, pady=10)
    frame_autoticket.grid(row=0, column=1, padx=10, pady=10)
    frame_waiting.grid_forget()

def request_token():
    """Function that runs in a separate thread to request token."""
    bls_at.request_discord_token(input_email.get(), input_password.get())

def on_login_complete():
    """Called once the login process completes."""
    lbl_discord_username.configure(text=bls_at.USER_NAME)
    change_wait_to_session()

def login_user():
    change_login_to_wait()

    # Start thread for request, then check its completion using after()
    thread_request_token = threading.Thread(target=request_token)
    thread_request_token.start()

    # Schedule a periodic check without freezing the GUI
    check_thread_completion(thread_request_token)

def check_thread_completion(thread):
    """Checks if the thread is alive, then schedules another check."""
    if thread.is_alive():
        frame_waiting.after(100, lambda: check_thread_completion(thread))
    else:
        on_login_complete()

btn_login = CTkButton(
    frame_discord login,
    text="Login",
    command=login user,
    width=LOGIN_ELEMENTS_WIDTH
)