I ran into the same error message when using #Predicate in SwiftData @Query with Xcode 26.0 beta 2, "Swift Language Version" Swift 6, and Setting "Default Actor Isolation" on MainActore (section Swift Compiler - Concurrency). Setting the "Default Actor Isolation" to nonisolated and inserting @MainActor above @Observable inside the code resolved the problem.

The answer from drct in "SF-Pro font issue with SF Symbols application" in Jan '24 might help: "The problem was that I had installed the newest fonts for all users (/Library/Fonts) but had previously installed the fonts for my user only (~/Library/Fonts). The fonts for users override the fonts for all users. Removing my user's fonts solved the issue."