Have confusions about websockets , Need help

I'll try to keep this short.
I have completed basic backend learning — CRUD APIs, middleware, routes, sessions, JWT, etc.
I thought I should learn WebSockets before starting to build full-stack projects.

Now that I'm trying to learn WebSockets, I'm finding it hard to locate any tutorials for WebSockets with Node.js. Almost all of them use Socket.IO. So, as usual, I asked ChatGPT, and it told me that Socket.IO is a library — basically a superset of WebSockets. It includes all WebSocket features but also adds extras. However, it also mentioned that Socket.IO isn't ideal for building large real-time apps because it's slower, and most big real-time apps (like WhatsApp) use raw WebSockets instead of Socket.IO.

So, I want to ask all the senior folks here: what should I learn?