I'm not exactly sure if this is the same issue, but from what I understand, collections, enums and other non-trivial value types are stored as binary data in CloudKit (you can check in CloudKit console) and their contents therefore can't be queried with a predicate.
It's also mentioned here: https://www.hackingwithswift.com/quick-start/swiftdata/using-structs-and-enums-in-swiftdata-models
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Community
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Swift Student Challenge
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