Getting UserDefaults notification changes in LSUIElement app

I have a regular app and an app with LSUIElement=YES. Both have Swift app lifecycle main entry points. Both have an app group "<TEAMID>.com.company.app". Both can read and write prefs and see each other's values.

But I can't for the life of me get changes from one app to notify the other. At first I tried NotificationCenter, but then learned (thanks to this thread) that you have to use KVO or Combine. I tried both. Both get the initial value, but never see subsequent changes.

Combine seems to just wrap KVO, looking at the stack trace.

I'm subscribing to updates like this:

    let defaults = UserDefaults(suiteName: "<TEAMID>.com.company.app")!
    defaults
        .publisher(for: \.enabled)
        .handleEvents(receiveOutput: { enabled in
            print("Enabled is now: \(enabled)")
        })
        .sink { _ in }
        .store(in: &subs)

…

extension UserDefaults {
	@objc var enabled: Bool {
		get {
			return bool(forKey: "Enabled")
		}
		set {
			set(newValue, forKey: "Enabled")
		}
	}
}

I'm writing to prefs like this:

    let defaults = UserDefaults(suiteName: "<TEAMID>.com.company.app")!
    defaults.set(enabled, forKey: "Enabled")

Am I missing something?