For the most part apps rely on Google for push notifications. I guess WhatsApp can handle its own notifications as SgtSurehand has said, so maybe try that.
But since you asked, there's pretty much nothing anyone can do about this. Google provides a push notification service and most app devs use it for Android phones because the vast majority of Android phones have Google Play installed and everything just works. Some devs add some backup code (like WhatsApp seems to do), but most don't.
Google makes it super easy for users to use their apps and app devs to program their apps to use their services. Unless a large number of people push for this to change, it'll just stay this way.
But I'd just like to point out it's possible WhatsApp notifications don't include any sensitive info in them, or they could be encrypted in a way that Google cannot read the data. I don't think Meta cares about our privacy, but I do think they don't want to hand personal data to Google on a silver platter either.