Same issue with example project from apple (https://developer.apple.com/documentation/swiftdata/adding-and-editing-persistent-data-in-your-app)

You have to add Item to MyItem after Init: class MyItem { var name: String var item: Item? init(name: String, item: Item) { self.name = name setItem(item) } func setItem(_ item: item) { self.item = item } }