I have a 64-bit Cocoa application that for legacy reasons calls Carbon function CancelMenuTracking to close an open menu. CancelMenuTracking is loaded dynamically from the com.apple.Carbon bundle.
The question is, why does it work (on macOS 10.14.4)? Pretty much all Carbon Menu Manager functions were documented as not available on 64-bit, before that documentation was removed.
Well, the simple answer is there's still bits of Carbon used internally in the frameworks — menus are definitely one of those areas — but that's an implementation detail and you can consider it a private API which shouldn't be used, just like CGS and others.