Developing Retro-GUI for Win3.11 (Delphi 1) and OS/2 (Visual C++) (2025)

What does this mean?

  In the end I’m now able to create applications using the same compiler and code-base for three different architectures (16-bit, 32-bit and 64-bit)

As mentioned earlier, he used the C++ v1.52 (1993) for Windows 3.x. It is a Pure 16-bit compiler. The resulting binary remains NE (16-bit). So, they cant generate a 32 / 64-bit Binary.