in my personal experience this popup notification is too intrusive and annoying/frustrating/stressful more if you receive several short messages and your screen will be often covered by that popup notification while you are trying to reply to someone in a chat, I always disable the “show notifications popup” for delta chat on android
is the sound played and the app icon shown in the status bar indicating that there is a new message? then that is more than enough IMHO
in general, iOS is not so bad in grouping notifications and in not annoying the user too much, not sure how much control one has about details as sound etc., many things are configurable by the user in the system settings. but yes, it has to be tested in practise
Telegram on iOS has custom in app notifications that have no sound and are made by the app, not handled by the system, at least during calls. they are more compact than the system notifications, maybe something like that?