On Windows, this was is implemented as SysWOW64. WOW64 means Windows on Windows 64. It makes the userland emulation and pretends towards the process that everything around him (incl. drivers) are the 32-bit ones.
Source: Microsoft.
https://devblogs.microsoft.com/oldnewthing/20081222-00/?p=19...
It's literally a 2004 game! That's ridiculous. A handful of opterons existed in the market, but Intel wouldn't get there for years still and it was well over a decade until x86_64 crossed 50% market share in consumer stuff.
Good grief, as it were.
Needless to say, annoying a bunch of HN nerds a quarter century in the future wasn't on Valve's radar. They just wanted some Mac revenue and picked the low hanging fruit.
What? First, those chips were plenty powerful to run HL2 (the game predates them). And second, all x86_64 chips can run older x86 32-bit code unmodified.
The reason macOS stopped supporting 32-bit code has nothing to do with the processors but more about them wanting to remove support for 32-bit binaries from the kernel and from all user-space libraries. To run a 32-bit binary, you need itself and all libraries it depends on to be 32-bit too, including the syscall boundary, which is "fine" (both Windows and Linux do this just fine, so it's really on Apple to have removed this). And I suppose Apple removed those because it was building towards a 64-bit-only world to simplify the Apple Silicon transition.
E.x. notebookcheck indicates that FEAR (released a yearish later) could get 20-30ish FPS at 640x480 but chokes at 1024x768 (at numbers matching the HL2 lost coast demo slideshow at 1024x768).
Gotta remember a lot of mac people were just happy to play something more modern than Marathon or Giants CK