It requires a google account though so I can't use it :(
I don't really understand why they insist on that as it doesn't seem to use google otherwise. I do have google play services, just no account logged in (which is not necessary for things like push to work!)
Because they get your profile picture, name, and email address when you click accept. I went through with it just to test, but definitely getting some data from its users.
Yep notifications require google play services installed. They do not require a google account or being signed in to one. It's based on the device ID alone. I don't have a google ID on my phone and push messages work just fine.
If you use on android apps from the playstore, most apps are built to relay their notifications through Google's Firebase Cloud Messaging (FCM), so they don't have to have a background notification listeners running 24/7. It also means less overhead from multiple notification listeners from every app having its own. So yes, if an app is built on top of google play services, it requires "google play services"
If an app says it doesn't rely on google play services, it uses an alternative notification listener or websockets, which might not be as effective, because Google is inbuilt and won't kill its own apps, the scale of its infrastructure, and its habit of listening on people's activity.
Add in Androids habit of killing background services, and you don't always get your notification when the app isn't in the foreground.
Even Signal from Playstore uses Google Play Services for notifications.
Well, Google firebase notifications do. Either Google play or something comparable like MicroG. It's possible to run them another way too but not many app backends support that.
But yes my complaint is exactly that this app requires google.