Thanks for your answer! But that doesn't explain why the Button(action:) works as expected, and why the layout is not recalculated if the view is removed.

Sorry, I think I made the mistake of accepting your solution. After a second thought and test, it seems that in your solution, the animation works only because you removed the .animation(nil) and the default modifier .offset() fires the animation under the hood. One testiment is that print("animating \(value)") is not executed.

to suppress the .offset()'s default animation behavier and make sure the interpolation of the animatable values happens in the RectView, i.e. the set { value = newValue; print("animating \(value)") } will be called and then check for completion of the animation.