Yeah user-created topics would be a fine enhancement. Various aspects of the multireddit concept have separate issues in the issue queue but they haven’t been coherently tied together yet. It might be time to do that.
One way to limit exposure to negative news is a keyword filter, which I implemented 6 months ago, early on in the project: https://piefed.social/post/7576
You might enjoy the book “Climate Leviathan”. It’s about all that and draws on a lot of history and philosophy.