Hello.I don't understand this : "The reason is that the simulator runs natively on M1 but the simulated app runs still under Intel". You are telling here that Xcode produce a x86_64 binary that runs on a arm simulator ? Hoe does that work ?

That looks like a bug to me, or undocumented bad side effect. That means that we should never modify NSLayoutConstraint.constant in the code... or else save the values and restore them in viewDidLayoutSubviews.

The app stays 5 sec in the background. It's definitely not killed (viewDidLoad is called once). Your second point is correct, however, it do work when Size Class variation is not used. It seems that the variation somehow forces the view to recalculate the layout every time the view appears, using the storyboard values.