Thank you. It seems obvious now, but after days of googling it wasn’t. the ‚Enable App Sandbox : Yes‘ does not apply to iOS. It‘s needed for macOS apps. I was stuck at level 1, but am now turned up to 11.

I set Build Settings: Signing: 'Enable App Sandbox' to 'No' . It works again. I had this problem suddenly after days of a functioning app, sandbox functioning for days before suddenly not.

Same problem here.