According to Apple, none of the 2012 MacBook Pro models are compatible with macOS Big Sur. See https://support.apple.com/en-gb/HT211238 So it is likely that, if you can get it to run at all, you will have unexpected problems.

What platform... macOS, iOS, iPadOS, tvOS?

I suspect your problem is with NSImage(byReferencing url:) Apple say: This method initializes the image object lazily and It does not attempt to retrieve the data from the specified URL or create any image representations from that data until an app attempts to draw the image or request information about it. and Because this method doesn’t actually create image representations for the image data, your app should do error checking before attempting to use the image I suggest that after... let image = NSImage(byReferencing: book.metadata.coverFile) ...you immediately check "image", and try to do something with it, to trigger the actual data retrieval. (It looks like just placing it in an Image(nsImage:) is not enough to do this.)

More information is needed. What is your camera? What format does it save images in?

You are not showing all your code, but it looks like... self.timer is a DispatchSourceTimer dispatchTimer(timeInterval:handler:) has no return type ...so your assignment of dispatchTimer() to self.timer will not compile (you are trying to assign a closure, when a DispatchSourceTimer is expected). Perhaps you intended? class func dispatchTimer(timeInterval: Double, handler: @escaping (DispatchSourceTimer?) -> Void, needRepeat: Bool) -> DispatchSourceTimer { Then dispatchTimer() could return "timer", and the assignment would work.

The receipt data is found at Bundle.main.appStoreReceiptURL, and contains information about all in-app purchases in the app. This property always exists in an App Store app. It does not exist in a sandbox app (Xcode or TestFlight). Apple say: This property makes no guarantee about whether there is a file at the URL—only that if a receipt is present, that is its location.

This is just my view, @Pete4Dev, But I don't think this is appropriate content for the forum. The forums are meant for code-level questions. Assuming your Salon app is a commercial product, are you trying to recruit app testers? Would it not be more suitable to do this on one of the many Freelancer websites? Or if you want people to test your app for free, then, well, I'm not sure where you would ask for that! Best regards, and no offence intended. (And of course, if Apple post here and say this is just fine and dandy, then okay.)

I cannot add my developer account to XCode This is the problem that you need to solve. Can you successfully log in to App Store Connect (using your Apple Developer ID and password)? If so, then it should be possible to add this account to Xcode If not, then no other method of uploading the app is going to work (You should build and submit your app using Xcode 13, for best results with iOS 15)

You say: func returnusername() That is, your function returnusername returns no value (called "void") But in returnusername, you say: return username So there is a contradiction, hence the error message. You probably mean: func returnusername() -> String

In their team on App Store Connect, under "Users & Access"... ...you need to have been added with the correct permissions (for the tasks that you need to do, on the app or apps that you support). Typically, this could be: Developer App Manager Admin Sometimes, "Developer" does not give enough access, in which case you may need to be "App Manager". Role permissions reference: https://help.apple.com/app-store-connect/#/deve5f9a89d7

No, you don't have enough space. Xcode needs a lot of free space to download, expand, and install. There are many threads about this issue, on this forum.

Has anything changed in iOS 15? https://developer.apple.com/documentation/ios-ipados-release-notes/ios-ipados-15-release-notes

Try: let floatValue = CGFloat(intValue)

You said; it looks like only GPS is used in core location Apple say (in the Core Location Overview): The framework gathers data using all available components on the device, including the Wi-Fi, GPS, Bluetooth, magnetometer, barometer, and cellular hardware. I can't answer your actual question, but I thought it might be helpful to point out that your initial assumption is incorrect.

There is a view that to become an "Expert" simply takes 10,000 hours of practice. Ideas are the easy bit, coding takes time and effort. I would suggest: Start small. Learn to code. Make small apps. Then make bigger apps.