Removing user default key DVTDeviceVisibilityPreferences fixes issue. defaults delete com.apple.dt.Xcode DVTDeviceVisibilityPreferences I had a wrong value type under DVTDeviceVisibilityPreferences key. String instead of Integer. Observed <key>2DDE32D1-C291-4C3A-A76F-2878C9F57F61</key> <string>1</string> Should be <key>2DDE32D1-C291-4C3A-A76F-2878C9F57F61</key> <integer>1</integer>

Thank you Ed, Issue report is created: FB15300340 FYI: Issue also reproducible when using Xcode 16.1 Beta 2 (16B5014f).

This is what we are doing: class EntryPoint: FIFinderSync { private var windowController: MainWindowConreoller? override func menu(for menuKind: FIMenuKind) -> NSMenu { let menu = NSMenu(title: "") menu.addItem(withTitle: "Example Menu Item", action: #selector(openMainWindow(_:)), keyEquivalent: "") return menu } @objc private func openMainWindow(_ sender: AnyObject?) { DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) { // [1] Switch to main thread !!! NSApplication.shared.activate(ignoringOtherApps: true) // [2] Activate App !!! let wc = MainWindowConreoller() wc.showWindow(nil) self.windowController = wc // [3] Retain window controller !!! } } } Working App example: https://objective-see.com/products/whatsyoursign.html https://github.com/objective-see/WhatsYourSign/blob/master/WhatsYourSignExt/FinderSync/InfoWindowController.m#L40

I was able to solve issue App containing System Extension to be activated must be in /Applications folder with build settings shown below: DEPLOYMENT_LOCATION = YES DSTROOT = / INSTALL_PATH = $(LOCAL_APPS_DIR)/MyDevelopmentApps SKIP_INSTALL = NO Idea behind, that the build product placed into a /Applications/MyDevelopmentApps directory instead into /.../DerivedData/.../Build/Products directory.

Removing a paired watch from iPhone simulator seems helped. But it is rather workaround :0

Same issue on my side in Xcode 12.3 (12C33). Seems a bug. At least po something prints to Xcode console in Debug Preview.

Same issue with XCode 12.3 (12C33). At last I can "print" with debugger breakpoints.

In Xcode 12.3, printing a log to Xcode's console seems still not working :( Messages sent with os_log or NSLog will go to system log (which can be viewed in Console.app).