If your home instance is federated with instances you don't want to see, you can use this script to remove all posts and comments from that instance without having to block communities individually.
Example:
Line 17: const blockedInstances = ["example.ml","lemmy.world"];
Edit the comma-seperated list on line 17 to the instances you wish to block. Add new ones inside quotes following a comma. Do not include https:// or trailing forward slashes in the instance text.
Wait, does the "block communities" feature in profile settings only block communities on the home instance? If so, that seems like a substantial opportunity for improvement.
Nope it can block other instance's communities. This script will block all posts at an instance level though, rather than having to keep adding blocked communities when people create more on that instance.