Multiline textbox

def gui_init():
    global textbox_my_textbox

    #----- LIVE PROCESSING BOX -----
    MonospaceFont = font.Font(family="Courier", size=10)
    textbox_my_textbox = tk.Text(
        root,
        bg="white",
        font=MonospaceFont,
        wrap = "word",
        height=8,
        width=50
    )
    textbox_my_textbox.pack(padx=10, pady=10)
    textbox_my_textbox.place(x=10, y=310)
    textbox_my_textbox.insert(tk.END, "Loading...\n")

Overwrite all text

    NewText = "Hello\nNew content"
    textbox_my_textbox.delete("1.0", tk.END)
    textbox_my_textbox.insert("1.0", NewText)

Multiline textbox that auto removes top line once full example

#*******************************************************
#*******************************************************
#********** ADD A LINE TO LIVE PROCESSING BOX **********
#*******************************************************
#*******************************************************
def textbox_my_textbox_add_line (new_line):
    global textbox_my_textbox

    #Get current line count
    LineCount = int(textbox_my_textbox.index("end-1c").split('.')[0])

    #Delete top line if we're over # lines
    if LineCount >= 7:
        textbox_my_textbox.delete("1.0", "2.0")        #Delete the first line (from line 1, char 0 to line 2, char 0)

    #Add a timestamp to the start of the new line
    #time_stamp = datetime.now().strftime("%H:%M:%S")
    #new_line = f"{time_stamp} {new_line}"

    #Add the new line to the textbox
    textbox_my_textbox.insert(tk.END, new_line + "\n")

    gui_update()