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On desktop Telegram may look like it's an Electron app, but it actually uses Qt

I suppose that on mobile they also don't use web technologies

The Telegram app is native: https://github.com/TelegramMessenger/Telegram-iOS

I think at least the android app is very much native

To my knowledge it is native on both android and ios and uses qt on the desktop (which is basically native on linux), but there is also a mac-native version.