Скрипт python (секундомер с графическим интерфейсом) работает на Windows 10. но не работает на Linux Mint Cinnamon

from tkinter import *
from datetime import datetime

temp = 0
after_id = ""


def tick():
    global temp, after_id
    after_id = root.after(1000, tick)
    f_temp = datetime.utcfromtimestamp(temp).strftime("%H:%M:%S")
    label1.configure(text=str(f_temp))
    temp += 1


def start_sw():
    btn1.grid_forget()
    btn2.grid(row=1, columnspan=2, sticky="ew")
    tick()


def stop_sw():
    btn2.grid_forget()
    btn3.grid(row=1, column=0, sticky="ew")
    btn4.grid(row=1, column=1, sticky="ew")
    root.after_cancel(after_id)


def continue_sw():
    btn3.grid_forget()
    btn4.grid_forget()
    btn2.grid(row=1, columnspan=2, sticky="ew")
    tick()


def reset_sw():
    global temp
    temp = 0
    label1.configure(text="00:00:00")
    btn3.grid_forget()
    btn4.grid_forget()
    btn1.grid(row=1, columnspan=2, sticky="ew")


root = Tk()

root.title("Секундомер")

label1 = Label(root, width=7, font=("Ubuntu", 42), text="00:00:00")
label1.grid(row=0, columnspan=2)

btn1 = Button(root, text="Старт", font=("Ubuntu", 12), fg='green', bg='white', command=start_sw)
btn2 = Button(root, text="Стоп", font=("Ubuntu", 12), fg='red', bg='white', command=stop_sw)
btn3 = Button(root, text="Продолжить", font=("Ubuntu", 12), fg='green', bg='white', command=continue_sw)
btn4 = Button(root, text="Сбросить", font=("Ubuntu", 12), bg='white', command=reset_sw)

btn1.grid(row=1, columnspan=2, sticky="ew")

root.attributes("-topmost", True)
root.mainloop()