Thinking that maybe I should be observing to NSTextLayoutManager.usageBoundsForTextContainer for changes through KVO, but it never seems to change so maybe not?

Ah, of course. The full name of Context was BrokenView<Something>.Context and in the place it was being used in the Preview it couldn't work out what the generic Something was. Thank you. I was bashing my head against it for ages

Thank you, that's working. One more question: in your example you explicitly set Enable-Private-Data for the app log category. Is it possible to enable it for all categories without having to list them all explicitly? thanks again

It's a Cocoa app running on macOS. Current OS is Ventura, and Xcode 15