As of v2.0.0 of ActivityPub for WordPress, you …

As of v2.0.0 of ActivityPub for WordPress, you can add this here code snippet to your WordPress site to stop it from silently accepting comment updates:

add_action( 'activitypub_handled_update', function( $activity, $second_param, $state, $reaction ) {
	if ( $reaction instanceof \WP_Comment ) {
		wp_set_comment_status( $reaction, 'hold' );
	}
}, 99, 4 );

That is, it won’t stop the comment from being updated, but it’ll require reapproval before it gets shown on your blog.

(I still don’t know what the second argument does exactly.) 🤣