I'd just like to interject for a moment. What you're referring to as macOS, is in fact, Darwin/macOS, or as I've recently taken to calling it, Darwin plus macOS. Darwin is not an operating system unto itself, but rather another free component of a fully functioning Unix system made useful by the BSD corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX.
Many computer users run a modified version of the Darwin system every day, without realizing it. Through a peculiar turn of events, the version of Darwin which is widely used today is often called "macOS", and many of its users are not aware that it is basically the Darwin system, developed by Next Computer.
There really is a macOS, and these people are using it, but it is just a part of the system they use. XNU is the kernel: the program in the system that allocates the machine's resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Darwin is normally used in combination with the macOS operating system: the whole system is basically Darwin with macOS added, or Darwin/macOS. All the so-called "macOS" versions are really versions of Darwin/macOS.
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Apple's engineers still refer to the OS as Mac OS X. Ventura is technically 10.18, despite the 13 major number in their marketing.
13.0 is not just a marketing number. It is the number stamped in the binaries produced with the Ventura SDK. It is the number in Ventura SystemVersion.plist. It is number used in the availability markup in the headers provided by the Ventura SDK. It is the number you use for runtime version checks when you use `#available` in Swift or `@available` in Objective-C. You will not find 10.18 in any of those build or runtime contexts (or anywhere else) because it is not the version number of macOS Ventura.
Many computer users run a modified version of the Darwin system every day, without realizing it. Through a peculiar turn of events, the version of Darwin which is widely used today is often called "macOS", and many of its users are not aware that it is basically the Darwin system, developed by Next Computer.
There really is a macOS, and these people are using it, but it is just a part of the system they use. XNU is the kernel: the program in the system that allocates the machine's resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Darwin is normally used in combination with the macOS operating system: the whole system is basically Darwin with macOS added, or Darwin/macOS. All the so-called "macOS" versions are really versions of Darwin/macOS.
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Apple's engineers still refer to the OS as Mac OS X. Ventura is technically 10.18, despite the 13 major number in their marketing.