YSK: You can block communities from appearing on your "All" feed. just go to the website of your instance, pull up the community, and click "block community" (On mobile click "Sidebar" first")
Why YSK: You may dislike, disagree with, or be tired of certain communities and don't want them in your feed.
I'm the same. I also block individuals who post the same thing in like 6 different subs. Yes those posts can tech ically belong in 6 different subs, but if I see more then 2 I just don't care and it's instant block from me.
Unlike subs where there's one centralized "Technology" sub for example, here they're spread out. There are at least 3 large and active "Technology" communities and so cross-posting to all is necessary. It's the equivalent to posting to the single "Technology" sub on the shit site. Therefore multi-communitu cross-posting is the norm here.