Apple has threatened to remove Amphetamine from the App Store

I am not a lawyer, this is not legal advice, but the App store may constitute an essential facility for a desktop program developed specifically for Apple Computers. https://en.wikipedia.org/wiki/Essential_facilities_doctrine

Sure, but they're not denying access to competitors. They're setting rules for use of the facility. "You can't promote illicit drug use in our facility" is a reasonable rule.

Whether the name "Amphetamine" does in fact promote illicit drug use may be up for question, of course, but that's got nothing to do with monopoly power.

There's no way this would apply here considering you can distribute Mac apps outside the Mac App Store.