It looks like there may be an environment variable set in your scheme. Can you check if something is there? Specifically OS_ACTIVITY_DT_MODE=1 or some other value? This will request Xcode use the old logging system and redirect os_log to stderr like this.

Great!! Yes, structured logging does depend on newer OS features and does therefore require iOS 17.0+ to function with structured logging. That also includes simulators so you will need to be on newer simulators. Thanks!