Typically tkinter is used with its own main loop that takes over the main thread. You need to run your app code off its callbacks or in a different thread. But you can also call tkinter to update from your own main loop without it taking over the thread.

ap_gui.py

from tkinter import *

#GLOBAL VARIABLES
root = None
lblStatus = None
txtEntryBox1 = None


######################
##### USING THIS #####
######################
#
##----- INITIALISE THE GUI -----
#ap_gui.gui_init()
#
##----- UPDATE THE GUI -----
#ap_gui.gui_update()
#if ap_gui.has_gui_been_closed():
#    print("Exiting main loop")
#    break
#
##----- UPDATE THE GUI STATUS TEXT -----
#ap_gui.gui_update_status_text("Running task...")



#************************************************
#************************************************
#********** CLOSE ROOT WINDOW CALLBACK **********
#************************************************
#************************************************
#User has clicked the windows close button
#We use this so tat we can set root to None and then test that from our main app to see if we need to close the app
def callback():
    global root
    
    root.destroy()
    root = None


#****************************************
#****************************************
#*********** BUTTON 1 CLICKED ***********
#****************************************
#****************************************
def btnButton1Clicked():
    global lblStatus
    global txtEntryBox1

    EnteredText = "You entered: " + txtEntryBox1.get()
    lblStatus.configure(text = EnteredText)



#********************************
#********************************
#********** INITIALISE **********
#********************************
#********************************
def gui_init():
    global root
    global lblStatus
    global txtEntryBox1

    root = Tk()                                     #Create the root window
    
    root.protocol("WM_DELETE_WINDOW", callback)     #Create callback for if the window is closed

    root.title("My app")
    root.geometry('350x200')                        #Set the window size width x height

    #Create status label
    lblStatus = Label(root, text = "Idle")
    lblStatus.place(x=5, y=170)

    #Create a Entry Field
    txtEntryBox1 = Entry(root, width=10)
    txtEntryBox1.place(x=5, y=5)

    #Create a button
    btnButton1 = Button(root, text = "Button 1", fg = "red", command=btnButton1Clicked)
    btnButton1.place(x=5, y=30)


    #Execute Tkinter
    #root.mainloop()            #<<<<This stalls execution of this thread here and hands it to the GUI until the window is closed
    root.update()               #For this app we are calling update in our main loop instead
    


#************************************
#************************************
#********** UPDATE THE GUI **********
#************************************
#************************************
#This needs to be called reguarly from the main loop to keep the GUI responsive
def gui_update():
    global root
    
    root.update()
    
    #Note there is also this function that can be useful in some situations as its less intesive than update()
    #root.update_idletasks()
    
    
    
#**************************************************
#**************************************************
#********** HAS ROOT WINDOW BEEN CLOSED? **********
#**************************************************
#**************************************************
#Call this from the apps main loop to see if we need to shutdown the app
def has_gui_been_closed():
    if root == None:
        return True
    else:
        return False
        
    
#********************************************
#********************************************
#********** UPDATE OUR STATUS TEXT **********
#********************************************
#********************************************
def gui_update_status_text(StatusText):
    global lblStatus
    
    lblStatus.configure(text = StatusText)
    gui_update()