Clarification about Firebase and @capacitor/push-notifications

Hi, I have a question about the @capacitor/push-notifications plugin. From the documentation Push Notifications Capacitor Plugin API | Capacitor Documentation it’s not clear to me if the “backend” is Firebase both for Android or iOs, or if in the case of iOs, I have to interact (server side) directly with Apple’s APNS.
I Ask this because - from what I understand -, Firebase is able to provide an unified interface for sending notifications to the devices, but it’s not clear to me if using this plugin it will work for both platforms.

You can use Firebase for both Android and iOS or just Android and interact with iOS directly with their APNs. I would just use Firebase for both.

Here is a good guide - Push Notifications - Firebase | Capacitor Documentation