You can also subscribe to [email protected] to see trending communities. Following the links to see the posts in the communities would be more discriminate.
I've seen a few. Blocked them now but they're out there. One of the biggest disappointments with reddit was all the good investment subreddits getting overrun and ruined. They're filled with people buying into blatant pump and dump or ponzi scheme crypto shit echo chambering buy X. It's just pure garbage.
What I do, is go to All, sort by whatever you normally sort by, and every time you see a community that you don't want to see, click the 3 dots and block it. At least that's how it works on the Jerboa app, sure there's an equivalent option in whatever you use. After a few days my feel cleared up a lot. I personally think that it's best if people do this vs defederation, but that's just my opinion.
In the Voyager app, I can long press on the community name on a post, directly from browsing in All, and select block from a pop up. It’s super quick and easy. Same pop up also has the option to subscribe.
In Memmy, go to the community, under the menu is an option to Block Community. It's kind of an endless game of whack-a-mole. My all feed has improved, but every day there's a few more I have to block. I like to check All occasionally to get of my bubble but it's a bit of a mess.
Not that Reddit's All feed is any good right now, which is at its absolute lowest quality I've seen in over a decade. Resembles instagram more than what used to be Reddit.
If you use the "Liftoff" app, there is a shortcut for blocking the community straight from a post in the feed. I think this makes that action easier in Liftoff than in most other apps.