Maximum DriverKit Driver Bundle Identifier Length is 64 Characters
If you get sysex didFailWithError: extension category returned error error when trying to Install Dext from Communicating between a DriverKit extension and a client app sample application, in Xcode change Bundle Identifier for DriverKitSampleApp and NullDriver to shorter ones, length should not exceed 64 characters.
For example, replace com.example.apple-samplecode.dext-to-user-client with com.example.dext-to-user-client- to make sure whole identifier is not longer than 64 chars, as suggested on Apple Developer Forums.