The things I miss from Reddit are mostly very niche. I left and haven't been back mostly because I refuse to use their BS app, and I refuse to see ads. I was a mobile Reddit user so I didn't use it on the computer much.
I do miss doing gaming giveaways of extra stuff for like animal crossing and so on. And I miss helping newbies with games (mostly retro gaming stuff). Other than that Reddit was a time sink for me and I have other places to use my time.
I don't get FOMO. I mostly miss interacting with other people. Talking about opinions. Finding people who agree with me about niche stuff. People don't seem to interact as much here and I don't think that's because of the lack of content.
But I don't see the point of going back to Reddit. The experience of trawling through the muck to get to a few grains of what I want just doesn't appeal to me. All reports I've seen suggest that it's just getting worse and I was struggling with the experience before the API debacle.