Thanks for those ideas. Now for a harder case, in which I need to do something of the form: var body: some Scene { if #available(macOS 13.0, *) { WindowGroup { AppView() } .defaultSize(CGSize(width: w, height :h)) .defaultPosition(UnitPoint(x: x, y: y)) } else { WindowGroup { AppView() } } } A SceneBuilder doesn't accept a control flow statement in its closure (like View does - your example earlier) var body: some Scene { WindowGroup { AppView() } if #available(macOS 13.0, *) { .defaultSize(CGSize(width: w, height :h)) .defaultPosition(UnitPoint(x: x, y: y)) } } Were this a View I could perform the platform conditional in a View extension using a ViewModifier to but there's no SceneModifier equivalent. My high-level challenge is to write a SwiftUI app that runs in macOS from Monterey to Sequoia, hence the need to condition out features missing in earlier generations.

As often happens, writing a question drove me to find my own answer. In this case, I wrote a sample using the new class "NetworkConnection" and (a) the documentation shows up in Xcode and (b) the new capabilities are not available before xOS 26.

To be honest, what I (and others) have wanted is concurrency in NWConnection I've provided that for myself, with suggestions from this Forum, with the following: extension NWConnection { func asyncSend(data: Data?) async throws { try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, Error>) in send(content: data, completion: .contentProcessed { error in if let error { continuation.resume(throwing: error) } else { continuation.resume(returning: ()) } }) } } func asyncReceive(length: Int) async throws -> Data { try await withCheckedThrowingContinuation { continuation in receive(minimumIncompleteLength: length, maximumLength: length) { data, _, connectionEnded, error in if connectionEnded { logger.log("←→ connection did end") continuation.resume(throwing: NWError.posix(.ECONNRESET)) } else if let error { continuation.resume(throwing: error) } else { continuation.resume(returning: data ?? Data(repeating: 0, count: 4)) } } } } } The significantly increased power and sophistication in NetworkConnection is welcome but my app's networking (with the above Extension) works from Monterey onwards. I will file a request in Feedback Assistant .. in fact, I'll file two! One to enhance NWConnection to support async and the other to have NetworkConnection operate in current, and older, systems. [ FB17963806 ]