The two most purely valuable experiences I have had on the Internet since 1995 are both simple forums dedicated to specific topics. Why do they work so well? I would have to say, the technology isn’t nearly as important as the moderation philosophy.
When we bought our house, there were electric radiators, and one was not working properly. A search brought up a site, http://www.radiateur-electrique.org. The surprise was, this is entirely peer operated, and the replies to my queries were both immediate and on point. This is low tech, circa 2005 forum software, but my problem was solved instantly. I can only assume that, while there are a few ads, there’s no business plan and somehow they’ve attracted members who help each other for the pleasure that brings. This forum is full of answers and exchanges of a constructive nature. Well done!
This is, in my opinion, an all-too-rare example of fulfilment of the promise of the Internet, circa 1993. I have gone back that forum for a different question and the result was the same. I have made sure that if I was able to contribute something, back I did so.
My experience with Mastodon is similar in that interest-focused instances seem to work better than the mostly unhindered noise of the larger instances that resemble Twitter (mostly) without the politics. So it feels like it is not the technology that can effect change, it is the center of gravity, commonality of interests.
My own best contribution to the online world is to not answer posts I don’t agree with unless there is an apparent usefulness to an answer, such as correcting some known fact.