Although you can of course use matrix for “general chit-chat”, my impression is that people use matrix differently then (say) the fediverse. The rooms that I find that have a lot of activity are mainly “support” rooms for a very specific purpose. Some of the tooms I am in that have a lot of activity are FreeBSD, python, rust, nextcloud, or specialised amateur-radio rooms like GNURadio, yota. etc.

A nice example of this is that the support-channel for lemmy is on … matrix.

As I see it, matrix is more a trouble-shooting tool like slack, discord, etc (threads, pasting screenshots, or pieces of source-code, a picture of your PCB, a video of what is on the oscilloscope, … )… while the fediverse systems are better for general chit-chat: short-messages on mastodon/…, longer threads on lemmy/kbin/… I do not think there is a contrast in this.