I my experience the battery life on degoogled devices is not that great since the apps have to run in the background in order to get notifications to work. We all know that google spies on the notifications on android but the question is: does microg do anything to protect your data? What data will google get about my notifications? If I’ve understood correctly google knows the metadata but not the content of the notifications as long as your messages are encrypted in the private messenger. That seems to be the case at least according to this article: Governments are spying on Apple and Google users through phone notifications, U.S. senator says
you really shouldn’t use microg - it does not provide any benefit over just using non sandboxed google play (if those are your only options).
It depends on how the app implemented notifications.
If you use one of the instant messengers we recommend, then yes, this is the case.