Python thread release

I running 2 thread in python and execute the function Do().

import sys, threading

def do():
    print ("Execute")

def run():
    def start_thread():
        thread = threading.Thread(target = do)
        thread.start()
        thread.join()
        return thread

    t1 = start_thread()
    t2 = start_thread()

run()
print('Press enter to Quit')
sys.stdin.readline()

After running the run() function, the threads t1 and t2 are out of scope. But, according to VS-Code, they are still in Running mode.

I wait for them to join(). This mean that they are terminated. So, how they are still running? How to release those threads safely?