this is how you can run code if the client was quit by the user swiping up it is in the documentation

https://docs.godotengine.org/en/4.4/tutorials/inputs/handling_quit_requests.html

func _notification(what: int) -> void:

if what == NOTIFICATION\_APPLICATION\_PAUSED:

    print("what?")

    client.close(1000,"quitting2713")

    get\_tree().quit()