piinats if you have Play Services, for prompt notifications you must install all your apps after it not before. You must then also grant Play Services a battery optimisation exception so that the connection to Firebase for push can be maintained.
Element from F-Droid, Telegram FOSS and Whatsapp use a websocket connection when given battery optimisation exceptions where Play Services are not present.
Session, Element from Play and Telegram from Play have a hard dependency on Play Services and Firebase Cloud Messaging for push as they do not provide a fallback like a websocket connection.
Hope this helps.