As someone who spent time writing a native slack alternative... It's massively more challenging to do so, and means that you won't have the exact same experience on different platforms. Auto correction etc. behaves different, font rendering, buttons, interactions, all different.

If I had to do it today, I'd look at egui, but I have concerns about its lack of UX (it's still early), or electron still, with a sane language (The wails project looked interesting too).