I'm looking for QNX 4 (<=4.12 I think) to ..

… install it in my old laptop 286 2MB. I’ve seen a QNX 32bit demo floppy, incredible, with X an Browser in a single floppy. ¿is QNX 4 16 bit version similar to this? ¿Where can I download a floppy demo?

You can’t.

There was an old 5.25 floppy demo version from the QNX2 days and the 32bit demo you are talking about. There was never any other demo versions.