Your driver can't match and out-score an Apple supplied driver until around 120 seconds after startup. Since there is an Apple supplied driver which recognizes IOMedia objects with GPT partition maps, that driver will always load, and IOKit will not load your driver, until after the 120 second time window. This behavior was introduced in macOS 10.14 - I believe for security reasons.

The lack of a macOS 14 installer is severely limiting our ability to test our applications and drivers with the new version of macOS. We do not have enough Macs to dedicate a separate test Mac for each of our test engineers just for testing macOS 14. Each new build of our products has to be tested on multiple versions of macOS; all of our products support macOS back to 10.14, some of them back to 10.12. In addition, we are completely blocked on testing on Intel Macs. Just some feedback from outside Apple's walled garden. Tim Standing VP Software Development Other World Computing, Inc.

Our solution is to install two copies of Xcode, version 15 and version 14.3.1. The older version is located at "/Applications/Xcode_14.3.1.app". Then the build script can just set the environment variable on the command line which causes xcodebuild: env DEVELOPER_DIR="/Applications/Xcode_14.3.1.app/Contents/Developer" xcrun xcodebuild build -configuration ......... This avoids the need for root access (which xcode-select requires) as well as ensuring that the older developer tools are only used for this one build step.

This is now being investigated by Apple. It turns out to have nothing to do with our kext as it occurs even without our kext loaded. It reproduces on Macs with Apple silicon.