Making an chatting website like telegram

So, i was just to build a website for chatting like telegram and i choose fastapi backend and reactjs frontend. Seriously, it was not simple to make this, i had to go through from many things and i also learn many things like websocket etc. I was wondering that making this is complex till this date so how whatsapp and other old chatting app made their systems. After spending hours coding i reach at a point where i think backend will be good at nodejs so i restart my project and build a new backend.