Great (though disappointing) information, thanks @eskimo. So the page you linked says HomeKit on Mac requires ADP membership. Assuming I join ADP, would I need to add the app to the App Store, or can I still sideload the app on my server? I don’t really want to distribute the app except to myself :)

Thanks for the detailed info, @eskimo! My app uses HomeKit (which is the reason I'm using Catalyst in the first place, since there is no native macOS API to my knowledge.) When I choose manual signing for the app, Xcode says it "requires a provisioning profile with the HomeKit feature." So, that seems similar to your comment about the keychain. In that case, am I then limited by the iOS code signing rules/dev account requirements? Incidentally the target machine is an M1 as well.