Earlier quoted context omitted.
The open source/degoogled alternative to that is UnifiedPush, did you take a look at this? https://unifiedpush.org/ https://ntfy.sh/
I did not, but I will. I would just point out that Privastead assumes the the push notification infrastructure is untrusted anyway.
I have no skin in the game of push notification infrastructure, but we've seen plenty of ShowHNs where a critical part of the Show is a total dependency on a 3rd party shim. While this isn't something like a dependency on a Twitter API that suddenly got yanked, it is still something that devs should really consider. Especially given theGoogs' track record.
Maybe this isn't the case it is a library deeply embedded in the Android ecosystem, but anytime a ShowHN mentions a dependency on theGoog it sets of the SpideySenses