If all code is in the original post then you have no place where you create your ModelContainer instance

That’s correct, you can’t use the unique constraint together with iCloud. I guess you need to add your own check to see if you need to do an insert or an update.

When I tested this I didn't use model(for:) since I already had access to the object and then isDeleted was set to true after the deletion. This looks like an issue with SwiftData that. you might want to file a report about but as far as real world programming goes your example code looks quite contrived and I don't see why you would want to do something like this.

Hi My question had nothing to do with the assert, I just wanted to understand the code better since the non-generic version worked and now I understand it better. I don't know if you are interested in testing this but I was thinking that maybe it's the associated type that causes the issues so one alternative to get would be to use MyModelProtocol instead for the generic type func addRecord<T: MyModelProtocol>(_ someDTO: T, recordName: String) async throws { ... }

A crash is exactly that, the app crashes immediately. When an error is thrown the app continues to run and can handle the error