Developer option are activated running an App from Xcode and disappears turning off the iPhone. Are you in this situation?

Ok. Quit/re open Xcode shouldn't be necessary; perhaps a deeper analysis by Apple with a Feedback Assistant could help. If developer option lastly appears after running an app from Xcode, please set above as valid answer for who will read.

As today works only with navigationViewStyle using column, or automatic, on iPad started in landscape, I filed a Feedback in Feedback Assistant with a sample project.

Would you provide a sample code?

I have had the same issue and thanks to your post I found that any not bordered, and not automatic or default, buttonStyle works correctly (that are: plain and borderless). Moreover the issue is absent on macOS.

Other is filled by the system and some app logs. To, temporally, clean up the "other" space, which don'l let me to perform an update on my iPhone 6s-16GB, I do: Backup (I do it on the Mac selecting "Back up all the data on your iPhone to this Mac") Delete everything: General / Transfer or Reset iPhone / Erase All Content and Settings Wait for the restart; the iPhone is as new. Login on appleseed.apple.com, download the iOS profile and restart (this step of course can be omitted) Restore from the backup. At this point the "Other" is empty.

The TestFlight invite code is sent by the sw developer from the App Store Connect of its testing sw. You should ask him/her.

On a try I found the solution: In the target / Build Phase / Copy Bundle Resources there were the files of the help book instead to the help book itself. I removed them. I removed the whole help book form the Xcode project. I recreated the book help hierarchy directly in the project file system; in the finder, not in Xcode. Finally, in Xcode, I added ("Add files to ...") the help book. This was recognised by Xcode as a bundle and added in the "Copy Bundle Resources" of the target.

Apple has prepared many tutorial, and more are available on internet (i.e. the Stanford lecture CS193p on YouTube). You could start from "Apple Developer", all WWDC tech talks and more, and Xcode.

Thank you Claude31 for your detailed explanation. You let my understand that the error in my simple example (from "Streamline your localised strings" in WWDC21) is the use of %d, which refers to 32bit integer, instead of %ld, which refers to 64bit integer. While I corrected the mistake, I realised that a widely portable stringsdict should have all theoretically possible values, i.e. "Order %d" (int, or 32-bit integer), "Order %ld" (long int) and "Order %lld" (long long int).

You can use pasteDestination(for:action:validator:) https://developer.apple.com/documentation/swiftui/tabview/pastedestination(for:action:validator:)

Thank you karanmisra for you explanation and interesting references. I'm going to improve my knowledge with unicode reports; anyway I filled a bug report.

Apple answer is: "the behavior you experienced is currently functioning as intended. The definition for NSWritingDirectionNatural has been different between AppKit & UIKit. With AppKit, the fallback direction for a content without any strong directionality is based on the primary localization. With UIKit, it’s LTR. We cannot change the behavior for AppKit since it requires a big amount of localization changes. If SwiftUI wants to use the UIKit behavior for AppKit, it should be using UIKit application context behavior."

Is a possibility to create a new tester group?

Which are the languages used for this testes?