How to list all registered MTurk notification settings in boto3

Boto3 update_notification_settings

Is there a way to list all notifications registered via boto3? I.e. notifications registered as follows:

import boto3

client = boto3.client("mturk")
client.update_notification_settings(...)

There seems no way to describe or list notification setting from HIT or HITType.

We can only use update_notification_settings() to creates, updates, disables or re-enables. When updated, the older notification is just replaced. (ref doc-boto3-v2)