An easy way to make code that uses UIImage cross-platform between iOS/tvOS & macOS

CrossPlatformImages.swift

// Either put this in a separate file that you only include in your macOS target
// or wrap the code in #if os(macOS) / #endif

import Cocoa

// Step 1: Typealias UIImage to NSImage
typealias UIImage = NSImage

// Step 2: You might want to add these APIs that UIImage has but NSImage doesn't.
extension NSImage {
    var cgImage: CGImage? {
        var proposedRect = CGRect(origin: .zero, size: size)

        return cgImage(forProposedRect: &proposedRect,
                       context: nil,
                       hints: nil)
    }

    convenience init?(named name: String) {
        self.init(named: Name(name))
    }
}

// Step 3: Profit - you can now make your model code that uses UIImage cross-platform!
struct User {
    let name: String
    let profileImage: UIImage
}

For future visitors: removing the convenience init allows this to function as intended. :)

I was a future visitor, and the advice by @wtpalexander has worked nicely. Thanks.