UPDATE It stopped working with beta 3, beta 4 is also not working for me. Can someone confirm that Live Activities show up on a physical device running beta 4? Any workarounds?

Have you tried the Swift Numerics package? Swift Numerics provides a set of modules that support numerical computing in Swift. https://www.swift.org/blog/numerics/

I have the same issue. I would also like to update the timer text label as soon as the timer counts down to 0. Using background tasks is not reliable enough for this use-case, as the timing of background tasks is up to the system and might only be called several minutes after the countdown has already expired. Using server-side push notifications for this simple and very common use-case also seems to be a ton of work that could be avoided. Something like Text(timerInterval: context.state.deliveryTimer, countsDown: true, timerEnded: "EXPIRED") would be quite nice.