There are still a ton of active forums in 2024, and some of them are active despite also having a Discord server available for the same community, so people are deliberately choosing it, rather than just using it because it's all that's available. That communication style isn't dead, and people still want it, and I still see new forums pop up that actually seem to get used.

That said, I feel like forums work best when they're actually about something in particular. I see people create new forums that don't have any actual point to them aside from the novelty of being a forum, and don't try to have any specific purpose, so they lose activity after that novelty goes away. And then they conclude that forums are just dead when they aren't, but starting a community is very hard (especially in 2024), especially one that doesn't know what it wants to be.

When there is actually a topic, people have a reason to join the community (to talk about that topic) and it gives the site a purpose, and I think a site needs purpose and a reason to visit. Social media sites seem to go for a selling point of "everyone is here!!" which is much harder to do when you are not able to attract millions of users and do not have the resources to manage a community with millions of users in it. A forum should try to be more like a club for a particular interest, which does work with a smaller amount of users.

To point to some specific forums I'd consider active, instead of just asking people to take my word for it:

https://forums.nesdev.org/ and https://www.smwcentral.net/ both have a forum as well as a Discord server and people continue to use both, and in nesdev's case I keep seeing people in the Discord server push to get important things documented on the forum and/or wiki so they're not exclusively on Discord.

I saw https://neoromhacking.net/ pop up and people seem to be using it, and it tries to fill a need people have. I don't use https://gbatemp.net/forums/ but I stumble onto it when looking for 3DS related stuff sometimes and I can see a ton of recent posts. Even the forums on the Neopets site are still very active and gets a bunch of posts every day.