Popped into Damus on my iPhone and the feed only shows people I follow. The only way to see non-followers is to go to the search tab, which shows all notes on the relays I have set up. If that's where you are going and seeing stuff you don't want to see, I don't know what to tell you...

The other possibility is that you have followed some hashtags. Doing so adds any post that includes that hashtag into your main feed. That will end up putting posts from people you don't follow into your home feed. Also, do you suppose malicious actors might add popular hashtags into their posts in order to get their content in front of people who don't want to see it?

Yep. They absolutely do. Unfortunately, this has made hashtags close to useless, unless you have a heavy web-of-trust or pagerank filter applied to them, which Damus does not... Imagine that, a censorship resistant protocol where it is actually difficult, to the point of being close to impossible, to censor.

I would recommend trying out Nostur instead. It has built-in web-of-trust filtering. Another good one is Coracle. No iOS app for it, as it is a web app, but you can use it pretty easily by first downloading nostr:npub1h0uj825jgcr9lzxyp37ehasuenq070707pj63je07n8mkcsg3u0qnsrwx8, then log in with your nsec and go to the built-in web browser and navigate to https://coracle.social/