How to resize window view dimension

I don't know if there are specifics for VisionOS.

But in SwiftUI, you can do this:

@main
struct MyApp: App {

    var body: some Scene {
        WindowGroup {
            ContentView()  
                .frame(width: 400, height: 400)
        }
    }
}

var body: some Scene {
        WindowGroup {
            ContentView()
                .frame(minWidth: 720, maxWidth: 1280, minHeight: 720, maxHeight: 1700)
        }
        .defaultSize(CGSize(width: 1280, height: 720))
        .windowResizability(.contentSize)

Will assign a default size. You can also limit the resize range with .frame(minWidth, maxWidth ...)