As far as I can tell, the version of #zap available through #yunohost is either old, or explicitly disallows federation through #ActivityPub.

I created a channel at @stuart (the only public zap instance that was working at the time), and it has a switch in settings for ActivityPub. I was also able to follow my channel here.

On my Yunohost instance, there is neither any mention of ActivityPub settings, nor was I able to follow that instance here.

I'm kinda disappointed...