Are you using the latest Sonoma/Xcode beta versions? With Sonoma beta 5 and Xcode beta 6 I’m not seeing this when building juceaide or the DemoRunner.
The JSON issue looks a bit familiar - I was seeing something like that with an older Xcode beta on Ventura, so i suspect there may have been a compiler bug. If you’re not using the latest beta, it’s probably worth updating and checking whether the issue is still present.
Other than that, we’ve got a couple of fixes for deprecated APIs in Sonoma that should be out in the next day or two.