Matrix supports threads (assuming your client implemented them) which work well for Q&A style rooms, but it doesn't have a full forum interface like Discord does. In Element, these threads are listed if you click the threads button in the top right, and you can browse them as a list.
However, using threads is entirely optional. In my experience, some people will use replies instead (of the "right click and hit reply" kind, not just a message below yours). That generally triggers a notification in most Matrix clients.
Most Matrix clients are built around chatting, either Signal/WhatsApp/Telegram/iMessage style with chat rooms, or Slack/Teams style with a collection of rooms per community.
Someone could use the Matrix protocol to build a forum (I've thought about doing that before), but it's not the default. Lemmy makes a bit more sense for support forums and such.