Do you want to write the app once or twice? Write it in SwiftUI and extend when SwiftUI doesn't fulfil your requirements. Swift/SwiftUI is the future. If you write it with AppKit you might have to re-write it later on.

And what code is it that's failing? Honestly, we cannot do anything without seeing any code. Why do people not get this?

Does the app launch and show the launch screen correctly? If so, I'd leave it as it is. The same thing happens to my apps. You can raise it as a bug if you want: https://feedbackassistant.apple.com/ then post the FB number here.

What do you mean by you "use the Mail function"? Do you mean the mail command (type it in the Terminal), or do you mean the Mail application? If you mean the application, then I'm afraid you're in the wrong place. These are the Developer Forums, where developers of apps for Apple's platforms ask each other for hints and tips on coding. Your question is more of a product support one, so I'd suggest you ask it over at the Apple Support Forums. Thanks.

This is not really something we random developers on here can handle - we don't work for Apple and have no access to their systems. The only thing you can do with your Apple Developer account is remove the user so they don't have access. What you need to do aside from that is make sure that developer has zero access to your code and systems. We don't know what systems you use, so that's for you to do, not us.

Microsoft may say that nothing has changed on their end, but that just means they haven't really checked. They're telling you they haven't changed anything in the OneDrive app, but if something in iOS/iPadOS has changed and it has adversely affected OneDrive then it is up to Microsoft to adapt their app to work with the new version of iOS/iPadOS. You should go back to Microsoft and raise a bug in their OneDrive app.

Well, the user could use Stacks on their Home Screen. Alternatively, can't you change the view on a button press?

A quick search yields this link. It looks like it doesn't delete your data. Read it through.

These are the Developer Forums, where developers of apps for Apple's platforms ask each other for hints and tips on coding. Your question is more of a product support one, so I'd suggest you ask it over at the Apple Support Forums. Thanks.

Two similar posts, two different usernames. Marking this as a duplicate.

Not really a question for us random developers. Your question is more of a product support one, so I'd suggest you ask it over at the Apple Support Forums. Thanks.

Once again, post some code!

Again, we can't really see what the issue is if you don't post any code.

We can't really see what the issue is if you don't post any code. For example, "My car doesn't work" tells me nothing about how I might possibly be able to help you.

These are the Developer Forums, where developers of apps for Apple's platforms ask each other for hints and tips on coding. Your question is more of a product support one, so I'd suggest you ask it over at the Apple Support Forums. Thanks.