In #Activitypub, replies to a post are a collection of links that are part of the original post. So it’s only natural that the original poster should be in control of what’s in the reply collection. Technically it’s quite simple to implement that the OP (original poster) can decide which replies he/she/they accept or refuse in said collection. It’s up to the developers of ActivityPub implementers like Mastodon et al to make that level of control accessible.