I am currently developing a SwiftUI app that I want to be cross-platform across majority of Apple devices (iPhone, watch, iPad, macOS). The application will share a lot of views and logic between iOS, iPadOS, watchOS and macOS.

What I want to do is make the app on macOS a menu bar application. In order to make the experience best for the user, apart from registering a menubar item I wanted to use a custom NSWindow instance that will be attached to a menubar item similarly to a NSPopover but will be able to detach when dragged outside and still maintain all the looks and feels of a normal NSWindow, like traffic light controls etc. It will be similar functionality to Cardhop, Fantastical and Harvest menubar apps.

What I find hard to do is using a custom NSWindow instance in combination with SwiftUI. I am using the latest SwiftUI and Xcode versions and probably can't downgrade, since I am on the new MacBook.

My Xcode version is 13.2.1 and macOS 12.1

What I tried doing to have a complete control over what is happening with the window, is resigning from @main tag on the SwiftUI App struct and moving that to NSApplicationDelegate instance I coded. I removed the SwiftUI App struct from the macOS target and tried adding the @main and @NSApplicationMain to my AppDelegate implementation, but it resulted in the AppDelegate not being run at all. App launched but nothing happened and nothing printed in the console.

I read on the internet that in the previous version it was possible to use the UIKit legacy lifecycle, which in my case could be helping me solve my case. Because I was unable to do it I tried hacking my way out of this situation.

My current solution is to still have the SwiftUI App struct instance as @main and adding @NSApplicationDelegateAdaptor with my AppDelegate implementation where I simply find the window that was started and run close() on it. This is a very hacky solution that I don't like but I can accept it if it is the only solution that will work at this time.

My question is two-fold:

Is it possible to completely resign from using the App struct and going with old-fashioned AppDelegate in the latest SwiftUI version? If it is not, how can I make WindowGroup use a custom extended NSWindow class that will add my functionality of attaching, detaching, arrow pointing to menubar item etc.

Thanks for help in advance!