you can't reference your object like this. The add_object_to_application method will put everything where bacpypes needs it. The thing you get back from this is an object that contains all the object you want to build....

device1['ZN-T'].presentValue = new_value

should work
And you don't need to clear_objects in your loop.

Also, have a look to the tasks (RecurringTask). This way you can create different functions to update the value of your objects and the execution will be automatically dealt by the task manager

    # extract from code...
    _new_objects.add_objects_to_application(weather_device)
    app = WeatherApp(weather_device)
    task_device = RecurringTask(
            update, delay=int(os.environ.get("OWM_REFRESHRATE"))
        )
    task_device.start()
    while True:
        await asyncio.sleep(0.1)

I'm not sure, but my instinct would tell me not to wait 5 seconds in the main loop as it could create delays in the responses BAC0 will give to other BACnet device talking to it. I know it is async code, but I'm pretty sure await asyncio.sleep will block for 5 seconds before continuing... (I may be wrong). Using a task will eliminate risks.