Comment by sneak
8 hours ago
Note that to send notifications to an iOS app, the app publisher has to send them. This means that they need to run an event forwarding proxy service (this is how Mattermost and Element/Matrix and presumably some/all of the ActivityPub clients do it), or selfhosting your server means you must also selfpublish your client app via the App Store and Apple’s developer program tax.
Safari finally supports Web Push so maybe you can bypass all that nonsense.
For Mastodon, each mobile app developer needs to have a "webpush relay server" to receive Mastodon's webpush notifications and transmit them to the platform's push service. For Android, Mastodon recently added support for the latest webpush standard which allows the app developer to directly register Google's webpush endpoint with Mastodon, removing the need for a relay. In all cases, push notifications are encrypted by the Mastodon server, and decrypted by the Mastodon client, so any intermediaries (relay server, push notification service) can not read their content.