When blocking communities, they will not show up in your “all” feed anymore. This makes browsing Lemmy nicer especially now that you might not subscribed to a lot of communities.
In the browser: In you Lemmy instance, click on your username (right upper corner), “Settings” and open the tab “Blocks” and type in the community you would like to block. Here you can also unblock communities
On Jerboa (Android): Open the community you would like to block, click on the 3 dotted menu (right upper corner) and click “Block Community”. Note: you can not unblock on Jerboa. Use the browser (Settings -> Blocks) to unblock.
I wish this worked. I blocked several communities that are either not relevant / interesting to me or are in a language I don’t understand, yet I still see their posts in “All”.
For example, I blocked the Formula 1 community three times already.