The software often seems old and clunky, or with the few newer options like discourse or nodebb, convoluted and bloated. But I think whats mostly missing these

The software often seems old and clunky, or with the few newer options like discourse or nodebb, convoluted and bloated. But I think whats mostly missing these days is amenities social networks have introduced like custom streams and filters. Forums in principle can do things like "Show all posts from user X" or "give me new topics that are tagged Y", but it often didn't even work way back when. A modern forum should allow to create custom streams to find and consume content and wrap that up in a nice package and these days of course, some form of federation should be possible, be it just RSS feeds or better yet cross posting etc.