Chat has not been around since the 90s, not in the form that is used today.
What's the feature of today's chat systems makes them qualitatively different from those that are 30+ years old?
The level of technical knowledge required to connect to IRC or a BBS in the 80s was far higher, which meant that only a tiny fraction of people bothered.
had most of the basic features of IRC.
I feel that the point made is a good one. Given that we can share what we want directly via instant messengers that everyone has "turned on" all the time, value proposition of Facebook drops dramatically. Anything you want to share you can share directly and immediately get it to whoever you want to see it.
In any event, the fact that chat programs are different or more common now doesn't mean they didn't exist in the 80s and 90s. IRC is and was chat as much as Slack or Discord are.
One of my first childhood memories was my brother showing me a real-time chat with someone in Germany. It was 1982. The letters appeared one... by... one... on the screen. It was probably a subconscious part of why I went on to study German later.