didSet not longer supported in observable?

I tried to migrate some code to SwiftData and Observable...doing this I wanted to mark a ViewModel-Class with @observable but get errors when using it in combination with didSet.

What's wrong with it?!

@Observable struct LADVAthletes {
    var queryName : String = "" {
        didSet {
            guard oldValue != queryName else { return }
            
            guard queryName.count < 2 else {
                athletesList.removeAll()
                return
            }
        }
    }
    
    var athletesList : [Athlete] = [Athlete]()
}

I get multiple Errors saying "Cannot find 'oldValue' in scope" "Instance member 'queryName' cannot be used on type 'LADVAthletes'; .... And so on...

What's wrong with it?!