Since the release of the iOS 15 beta version, Telegram has stopped receiving push notifications in a timely manner.
The way iOS works is that if the app is completely closed, a push notification comes in about a minute, but if it is open and minimized, the notification comes almost instantly.
However, over the last 2 years, Telegram has not sent notifications on iOS in a timely manner, making the user wait for up to a minute (and sometimes not even sending a notification at all), and this is something users with different iPhone models, iOS versions and Telegram clients face. Inside the app, however, notifications are timely.
By comparison, the MacOS version of Telegram receives notifications almost instantly, not containing the problem of its iOS counterpart.
All other apps send PUSH notifications in a timely manner.
The problem lives on to this day on the latest current iOS 16.3.
P.S. A user once reported in a group that Pavel Durov had personally pointed out the problem and promised to fix it.
iOS 16.3, iPhone 13 Pro, TG-iOS 9.4.1 (25132)