Collecting 16k is not possible in the demo version of the game. This is entierly my fault, and a consequence of the cursed development cycle of this game.
As a workaround, there is a cheat to unlock it. Open the console with F2, and type in "skip drag2" and press enter. That will satisfy the criteria for unlocking that ending.
I don't want to update the demo again, since I risk breaking it even worse, consider this the intended sollution for now.