I have a Workout that has an inverse RelationShip with Exercise:

@Model
class Workout: Identifiable {
    var id: UUID
    var name: String
    @Relationship(deleteRule: .cascade, inverse: Exercise.workout) //when deleting a workout you delete all exericses that happened during that workout
    var exercises: [Exercise]?

@Model
class Exercise: Identifiable {
    var id: UUID
    var exerciseName: ExerciseName
    
    @Relationship(deleteRule: .cascade, inverse: MySet.exercise)
    var sets: [MySet]?    //When an Exercise gets Deleted all Sets associated need to get deleted

    var date: Date
    var workout: Workout

Then In another view I pass a workout and create a new set with that workout as a Parent:

Button {
                if(selection != nil) {
             
                    let newExercise = Exercise(id: UUID(),exerciseName: selection!, date: workout.endTime, workout: workout)
    
                     modelContext.insert(newExercise)
                    
                    let set =  MySet(id: UUID(), weight: 0, reps: 0,isCompleted: false,date: Date.now ,exercise: newExercise)

                     modelContext.insert(set)
                 
                    dismiss()
                }
                
            } 

this shows up straight away on the editworkoutview but when I go back to my workout list view I need to refresh the app to see the number of exercises a workout has. that view queries workouts and then I use its exercises to see the number of exericses that workout has:

    @Query(animation: .easeIn) var workouts: [Workout]

 ForEach(workouts) { workout in
                    NavigationLink(value: workout) {

if let exercises =  workout.exercises {
                                    Text("(exercises.count)x Exercises")
                                        .font(.system(size: 13))
                                }

The Text only displays the correct amount of exercises when I refresh the app.