MacCatalyst Multi window App not calling Scene Delegate

On Mac Catalyst, windows do not become inactive when they lose key, and do not become active when they become key or frontmost. As such, you can’t use scene active/inactive callbacks to follow this state.

You might want to follow the key status of your UIWindows instead. Use UIWindow.didBecomeKeyNotification and .didResignKeyNotification to keep track of this state.

You can observe the activeAppearance trait. Try this:

final class ViewController: UIViewController {
    @IBOutlet weak var statusLabel: UILabel!

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        updateWindowStatusLabel()
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        if previousTraitCollection == nil || previousTraitCollection!.activeAppearance != traitCollection.activeAppearance {
            updateWindowStatusLabel()
        }
    }

    private func updateWindowStatusLabel() {
        if traitCollection.activeAppearance == .active {
            statusLabel.text = "Appears active"
        } else {
            statusLabel.text = "Appears inactive"
        }
    }
}

I fixed the layout reversion issue by calling my method that mods the layout constraints from an override of viewDidLayoutSubbviews in each affected VC

For the moment, I am sticking with the NSWindowDidBecomeMainNotification event to trigger activation events in my viewControllers, despite the slight increase in overhead by observing the event in all open VC.