After some time and some investigation, there are AT LEAST 3 different versions of Knight Force EGA/VGA out there:

The 3.5" floppy I got from Spain, if the original floppy is not in the drive, the game will start but without sprites and stopped time.
Hash(MD5): 466fa9a5a836bee8d6177cc29ef90432

The 3.5" floppy of Spieler8: it spits the message "invalid disk ..." if the original floppy is not in the drive and it doesn't start at all.
Hash(MD5): 0d8e67c7ce0f9a7488be0230cc2c531f
Side note: there's a Prehistorik2 version out there that works the same way. The executable is available, it's not packed in .sqz and it doesn't start if the original disk is not in the drive.

Two 5.25" floppies version: if the original floppy is not in the drive, the game will start but without sprites and stopped time.
Hash(MD5): fb3211f2c311845311ecb9f410146134

ending scene not triggered

Scratch what I said earlier: I managed to finish the game! If you see the main character and enemies, you can finish the game.
There are no hidden switches or variable set imho.