I have read multiple similar questions & answers, but somehow still have not understood how to apply them to my particular use case. The best I found was using Tkinter with Thread:

from Tkinter import *
import threading

class App(threading.Thread):

    def __init__(self, tk_root):
        self.root = tk_root
        threading.Thread.__init__(self)
        self.start()

    def run(self):
        loop_active = True
        while loop_active:
            user_input = raw_input("Give me your command! Just type "exit" to close: ")
            if user_input == "exit":
                loop_active = False
                self.root.quit()
                self.root.update()
            else:
                label = Label(self.root, text=user_input)
                label.pack()

ROOT = Tk()
APP = App(ROOT)
LABEL = Label(ROOT, text="Hello, world!")
LABEL.pack()
ROOT.mainloop()

But here the parallel task is the raw_input, which is already part of the App itself. But what if I want to have instead two instances of App each in its thread running in parallel? Or App + open3d visualization? How would I modify this code to have responsive Tkinter GUI in one thread, without explicitly relying on some function input?

Another solution I found utilized Toplevel. Is that indeed the correct approach for this problem? Would it not complain that Tkinter does not like working with threads, as multiple other answers to similar questions pointed out? Example:

from tkinter import *
import threading
import time

class Show_Azure_Message(Toplevel):
    def __init__(self,master,message):
        Toplevel.__init__(self,master) #master have to be Toplevel, Tk or subclass of Tk/Toplevel
        self.title('')
        self.attributes('WM_DELETE_WINDOW',self.callback)
        self.resizable(False,False)
        Label(self,text=message,font='-size 25').pack(fill=BOTH,expand=True)
        self.geometry('250x50+%i+%i'%((self.winfo_screenwidth()-250)//2,(self.winfo_screenheight()-50)//2))

    def callback(self): pass

BasicApp=Tk()
App = Show_Azure_Message(BasicApp,'Hello')
for i in range(0,2):
    print(i)
    time.sleep(1)

App.destroy()