So a few optipna (I'm on kbin but similar):

• move to an instance where the users aren't signed up to those communities (remember All is not the whole fediverse, All is just the content that is local to that instance plus that users on your instance have subbed to. On a big instance you will see a lot in all)
• block individual communities or entire instances. I have been blocking the numerous meme communities for example which tidies up my All feed, but it is tedious as there are so many
• browse Lemmy or Kbin using Subbed instead of All or Local views. On kbin you can do that by going to /sub, clicking the link on the toolbar or setting it as your default view.
• create your own personal instance of lemmy or kbin and only sign up for content you want on that aerver. You can browse new communities to join via other instances then add it to your instance.