Nope! Both are fully native macOS apps, at least on the version of Monterey that I'm running.

You can examine which frameworks a binary links by running `otool -l /System/Applications/Photos.app/Contents/MacOS/Photos`. Traditional macOS Cocoa apps will link AppKit, while Catalyst apps will link UIKit.

For example, if you run that command with a Catalyst app (e.g., Messages or Maps), you'll see that those apps link against `/System/iOSSupport/System/Library/Frameworks/UIKit.framework/Versions/A/UIKit`, and AppKit is nowhere to be found.

Photos on the Mac actually uses their own private reimplementation of UIKit called UXKit from before Catalyst.

(So does Twitter on the Mac, which was written by a developer on the original iPhone.)

The new Twitter app does use Catalyst though.

Interesting, I thought I had heard that App Store was Catalyst now for some reason.

It does kinda look like a Catalyst app, with its navigation stack, whitespace, etc.