Xcode – State of an instance is not updating — SwiftUI

So I have this structure Task which has a @State completion:

struct Task:Identifiable{
    var id: Int
    @State var completion:Bool = false
    var priority:String? = nil
    @State var completionDate:Date? = nil
    var creationDate:Date
    var fullDescription:String
}

In a TaskItem:View I’m trying to make a checkbox that will update the state properly:

struct TaskItem: View {
    
    @State var task:Task
    @State var isChecked:Bool = false
    
    func toggle(){
        isChecked = !isChecked
        task.completion = isChecked
        if isChecked {
            task.completionDate = Date()
        } else {
            task.completionDate = nil
        }
    }
    
    var body: some View {
       
                    Button(action: toggle){
                        
                       Image(systemName: isChecked ? "square.split.diagonal.2x2": "square")
                        
      
            
            
        }
        
    }
}

But even though isChecked changes and the image as well, the task.completion doesn’t. How can I fix this?

I’m currently using this to view it:

struct TaskItem_Previews: PreviewProvider {
    static var previews: some View {
        let task =  testTask()
        TaskItem(task: task)
    }
}