@JohnBloor

I'm not sure there's a way to block boosts of replies specifically. I assume you mean the Home timeline?

You can hide boosts, and you can hide replies, but as far as I know you can't narrow this down to just boosts of replies.

On your server's website, you can hide boosts or replies by clicking the slider icon in the top right corner of the Home timeline. You will still get notifications of replies that mention you, and you will still be able to see replies in threads.