As per new notification from apple before April 1, 2021 all app needs to use HTTP/2 based APIs, as we are using FCM for cloud messaging, need confirmation that firebase services will work fine in the future as well,
The HTTP/2-based Apple Push Notification service (APNs) provider API lets you take advantage of great features, such as authentication with a JSON Web Token, improved error messaging, and per-notification feedback. If you send push notifications with the legacy binary protocol, we strongly recommend upgrading to the APNs provider API.
To give you additional time to prepare, the deadline to upgrade to the APNs provider API has been extended to March 31, 2021. APNs will no longer support the legacy binary protocol after this date. https://developer.apple.com/news/?id=c88acm2b