This helped a lot.I missed just this line, because I had wrapped the options in a var and forgot to finally apply the option to the "cloudStoreDescription".cloudStoreDescription.cloudKitContainerOptions = NSPersistentCloudKitContainerOptions( containerIdentifier: "iCloud.com.mydomain.mycontainer")

This will deselect all annotations, which have been previously selected. let selectedAnnotations = mapView.selectedAnnotations for annotation in selectedAnnotations {       mapView.deselectAnnotation(annotation, animated: false) // better to animate selection, since deselection could be many }

This seems to get ridiculous: we're all in home office and Apple can't make sure the internet connection stays stable? All I read here seems not to fix this problem and the checked solution is the sys feedback page from Apple - posted 6 months ago? I have 4 Macs and those running Big Sur have these unstable connections. The one with Catalina does not. Apple, hello? Anyone home?

This problem still exists with Xcode 12.4 !