I was just talking with support and downloaded the new beta and my IPAD still has no sound on astc 3.0 channels but i found this
https://developer.dolby.com/platforms/apple/ios/overview/
AC4 maynot be support on older idevices.even if they are on ios 14 basicly any idevice before 2018.
i sent this to support.
And that the beta on my Iphone 11 works with audio