Free accounts can have at most 5 devices associated IIRC. You can manage your registered devices on the Certificates, Identifiers & Profiles - https://developer.apple.com/account/resources/devices/list page.

I can only answer 1, and the answer is that indeed Apple will not take a cut from the revenue because the service or good delivered is outside of the app.

What Roshan Joy said is correct. The website that customers go to is reportaproblem(dot)apple(dot)com

For a SwiftUI macOS App, I came up with this solution to enter full screen. In my use case I want the app to go full screen immediately on launch, but you can do this at any point. import SwiftUI @main struct MacApp: App {     var body: some Scene {         WindowGroup {             ContentView()                 .onAppear {                     DispatchQueue.main.asyncAfter(0.1) {                         if let window = NSApplication.shared.windows.last {                             window.toggleFullScreen(nil)                         }                     }                 }         }     } }