They whitelist the above apps from their battery management systems and indiscriminately terminate everything else.
Summary - figure out how to whitelist telegram on ur phone and you should be fine.
[1] https://support.signal.org/hc/en-us/articles/360007318711-Tr...
Personal anecdote: even Google have been wishy-washy between different versions of Android when it comes from battery optimizations (Android 6/Marshmallow is the most hardest on this front), but at least it was documented. Imagine the pain of managing other brands (and it seems that all Android manufacturers engage on it one way or another).
Edit: in 2018, VideoLAN/VLC complained that Huawei agressively kills apps outside of its whitelist (https://twitter.com/videolan/status/1022033608670961665). There is no update on this one unfortunately, but I've heard that it was fixed in subsequent EmUI versions but there is no verification of that from VideoLAN or Huawei.
Edit edit: Unrelated to the notfications issue, benchmark scores are allegedly being tricked out by a certain chip manufacturer running the chips out-of-spec in a whitelist (https://www.techarp.com/mobile/mediatek-benchmark-cheating-2...).
But I had this whole reply typed up for iOS so, may as well include it:
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I can only speak for iOS, but it definitely doesn’t work this way on iOS.
The ability to run in the background is something you can grant to any app, and there’s no special treatment of any one third party app versus another.
It’s not unlimited though even if you do grant the permission... if they use too much memory in the background they may be killed, and there’s a limit to how long they can stay running in the background.
Push notifications are supported anyway, because the apps servers are supposed to deliver push notifications to APNS, which delivers them to your phone on behalf of the app even if the app is closed.
But the transition from “app is running in the background and notifies you” (which can’t last forever) and “app is killed but the server delivers a notification through APNS” (which works when the app is dead) is often implemented poorly by developers and isn’t seamless. It’s hard to get it right.
But no third party apps get treated any different in this regard.
I want every app I don't manually allow to run in the background to be terminated after a short period of 30s~60s or so.