When you block a user, they lose the ability to direct message you.
They also lose the ability to react to your posts.
I think blocked users should still be able to react to posts by the blocker. Obviously, they should not be able to react to posts in a direct message. But within a server, they should be able to react to any post, regardless of whether the user is blocking them.
Also, you might add a feature where users can choose not to be able to see reactions from people they have blocked. This would allow them to ignore harassment, while others can still see how the post has been reacted to.