Also, Mac is a moving target. Each year, there is a new version that is basically its own little snowflake, with older things deprecated and newer things added.

Windows 11 will still run Windows apps from Windows 3.1, because they have a backwards compatibility effort that Apple eschewed.

Now that makes it more complex to emulate all the features, but the core features used by most programs get emulated, and then just add features for specific programs to get them to work. And games tend to use core features and DirectX or OpenGL, mostly, whereas productivity apps and other things can do lots of weird things that are non-standard.

For Mac OS X, you really need to handle each versioon of Mac OS X. There are some core features that may work across versions, and some features that are available only on certain versions, then some features that are unique.