Дело не в количестве поддерживаемых окон, просто gui-редактор не спроектирован в моей голове!
import tkinter as tk
from tkinter import ttk

def open_new_window():
# Create a Toplevel window
new_window = tk.Toplevel(root)
new_window.title("New Window")
new_window.geometry("300x200")

# Add widgets to the new window
ttk.Label(new_window, text="This is the new window!").pack(pady=10)
ttk.Button(new_window, text="Close", command=new_window.destroy).pack(pady=10)
def else_open_new_window():
# Create a Toplevel window
new_window = tk.Toplevel(root)
new_window.title("New Window")
new_window.geometry("300x200")

# Add widgets to the new window
ttk.Label(new_window, text="здесь некоторый текст").pack(pady=10)
ttk.Button(new_window, text="Close", command=new_window.destroy).pack(pady=10)

# Create the main window
root = tk.Tk()
root.title("Main Window")
root.geometry("400x300")

# Add a button to the main window to open the new window
main_label = ttk.Label(root, text="This is the main window.")
main_label.pack(pady=10)

new_window_button = ttk.Button(root, text="Open New Window", command=open_new_window)
new_window_button.pack(pady=10)
new_window_button = ttk.Button(root, text="Open Second Window", command=else_open_new_window)
new_window_button.pack(pady=10)


# Start the Tkinter event loop
root.mainloop()