> The idea was that Windows, as a 16-bit operating system, could run a subset of Win32 apps that were compatible with the Win32s API surface.

386 mode in Windows 2 (sold as Windows/386) and 3 was really a 32-bit operating system for 16-bit applications.

Win32s allowed some 32-bit apps to run on windows 3.1 and up. Including many versions of Internet Explorer (Microsoft also released ie as a 16-bit application, though).