The bug number is FB11995593.

Thank you! This solved the problem for me as well.

Thank you for your suggestions - appreciated! They both work and a slider with isHighlighted = false looks basically like a disabled slider (you can check the appearance by setting the slider initially to isEnabled = false. I am still wondering why sliders appear to need extra treatment while other UI elements change their appearance immediately as a reaction to a change of isEnabled. Btw, something similar seems to be going on with sliders in SwiftUI where a simple .disabled(boolStateVariable) does not work while .disabled(boolStateVariable).id(boolStateVariable) does the trick. I am inclined to file a new entry in "Feedback Assistant" but unfortunately my recent experience has shown me that such a feedback just sits there in the "Open" state.