broker_address= "mqtt.googleapis.com"
port = 8883
client = mqtt.Client(client_id='projects/<project_id>/locations/<location>/registries/<registry_id>/devices/<device_id>',
        protocol=4)
password=create_jwt(...) #works
client.username_pw_set(username='unused',password=password)
client.tls_set(ca_certs=<route_to_cert>, tls_version=ssl.PROTOCOL_TLSv1_2)
client.on_connect = on_connect
client.on_disconnect = on_disconnect
client.on_message = on_message
client.on_subscribe = on_subscribe
client.connect(broker_address, port)
client.loop_start()
while connected_flag == 0: #changed in "on_connect" method
    print("Wait until connected ", connected_flag)
    time.sleep(1)
print("Connected")
topic = 'projects/<project_id>/topics/<device_id>'
client.subscribe(topic)
while subscribed_flag == 0: #changed in "on_subscribe" method
    time.sleep(1)
time.sleep(5)
client.loop_stop()
client.disconnect()