I just started my de-googling journey recently, and so the mechanics of notifications were still unclear to me, and I found this video super helpful.
It explains how most mobile messaging apps (including privacy-focused ones like Signal) rely on Google and Apple’s centralized servers to deliver push notifications, which exposes vast amounts of user metadata.
Here’s the YT link, for people who prefer it: https://youtu.be/c3ennD3wKn0
From what I recall, Google would be able to see our device received a notification and when but not the actual message nor sender/recipient identity.
I think that’s fine for my threat model.
Molly seems like a potential alternative though since its a signal fork and supports UnifiedPush so you can choose a different notification supplier
They see cintents if the contents is displayed in the notification