UIBarButtonItem(title:image:primaryAction:menu:) not available in Mac Catalyst?

Now that my app is in the App Store for iOS and iPadOS, I'm trying to go for the trifecta using Mac Catalyst.

Specifically, I'm trying to invoke UIBarButtonItem(title:image:primaryAction:menu:), and when I've checked the magic Mac button in Deployment Info (invoking Mac Catalyst), the compiler is complaining about this statement:

Code Block UIBarButtonItem(title: "Files", image: nil, primaryAction: nil, menu: leftItems)

saying that it "Cannot convert value of type 'UIMenu' to expected argument type 'Selector?'.

There's another form of UIBarButtonItem's initializer that does want a selector -- and I'm using that elsewhere -- but the documentation states that this method *is* available for Mac Catalyst.

What's going on?

Thanks for any help.