I kind of hijacked another Swift/SwiftUI posting (sorry!) because of problems with documentbased SwiftData projects - here is the answer in a new thread, just in case someone is running into the same problems.
(link: My recent experiences with Swift and SwiftUI)
What I did:
I tested my Swift/SwiftData apps on a iOS 18 test-device, before updating all my production devices. My MacBook was on macOS 14 while testing.
Results:
While every SwiftData app (with/without iCloud Sync) worked perfectly, none of the documentbased SwiftData apps did run. There was just a white screen, no action possible. For testing, I have an older iPad, updated to iOS 18.
Solution:
The solution is really easy: Just deploy the apps with Xcode 16 and all documentbased apps I tested are fine!
I finally got an older MacBook that I could update to Sequoia, installed Xcode 16, attached the test-device - and voila!
I was really afraid because I found blog-posting saying things like ‘unless You’re very happy, there might/will be issues after updating…’. I have 3 important (for me) documentbased apps and I re-created 2 of them as ‘normal’ SwiftData apps, just in case.
Due to some other (FileMaker) projects I have to support, I could not update my MacBook to Sequoia earlier