Yes this works quite well. I have been using it to allow commenting via the Fediverse to a Wordpress RSS feed syndication page with this excellent Feed Aggregator plugin.

For more Wordpress-related ActivityPub projects and other plugins, check the the ActivityPub Developer Resources Watchlist (I am a co-maintainer, ping me if you know about additional stuff to add).

The plugin is great and with mastodon and misskey it works great. If the blog comments are closed, in some cases it is not enough to approve, but you must approve the comment by making any changes to it (from the wordpress moderation panel).

Personally I encountered a problem with Friendica: since Friendica has native support for following RSS / ATOM feeds, it seems that the RSS protocol prevails over the wordpress / activitypub one. I don’t know how this can be resolved …

The only sore point is this: I would like to point out that, with this plugin, a private/direct message is not reported in a particular way and therefore, once published, it loses its privacy attributes. Also, if the user deletes the message, the unsubscribe message is not accepted by the plugin and the message still remains crystallized for eternity in the form of a comment in the WordPress blog. This of course happens even if the message is a direct message, therefore the highest standard level of confidentiality existing today in the social networks of the fediverse. Having said that, for a principle of caution related to privacy, I will disable the plugin pending further changes; however I believe that the activitypub for wordpress plugin is a beautiful project and that it deserves further development and possibly further financial support; in fact, the path taken is good and contributes to making the web more beautiful and similar to the decentralized spirit of the origins