Most importantly, it's bad at protecting my privacy. You can't show any message to anyone on your screen or have someone look over your shoulder unless you want them to see who you recently communicated with in what order as well as the start of the most recent messages.
Thanks for mentioning that. I always wondered why there's no option to at least hide the most recent messages and dates (or temporarily hide the whole sidebar). I guess most people are either fine with it or use their phone instead (and using Signal-Desktop in public / when someone's looking is probably uncommon). It seems like at least Telegram-Desktop has this issue as well (not sure if there's an option for it).
Anyway, a slight modification to the UI to hide/minimize the sidebar would be something I'd appreciate for those rare situations.
Native: https://macos.telegram.org/
Qt client: https://desktop.telegram.org/
In addition, there’s a libpurple plugin should one want to use Telegram with Pidgin, as well as several other clients including one that’s TUI based.
The choice of client is a massive boon. It’s unfortunate that one can’t use a alternative Signal clients, because they’d likely solve many of the gripes people have with Signal.
There are many really good Electron applications, Visual Studio Code being one of them.
The Signal desktop app is Electron, where as Telegram is native. That's why and it's that simple.