It's kind of interesting that we're in a place where the Apple CT APIs are a precondition to people attempting serious contact tracing from the app layer.

iOS has made the UX so difficult for straight background location tracking that you kind of can't build that app without it

There are counterexamples, like the Singapore app "tracetogether," but afaict if you have an iPhone it requires you to walk around with the app in the foreground and the device unlocked in order to function. If that's true, I kind of wonder about the real adoption of that app.