Hi! I played the demo and bought the game after.. However, it won't download on the itch app, I tried downloading it on safari and that worked. But I am unable to open the demonheart app on my Mac. Can you help me in some way? What am I doing wrong? 
thanks! 

Hello. So, the demo works for you, but the full game does not? I've been checking the files, and it looks like the demo is just missing the last 4 chapters, the rest should be the same. If the demo can start up, you could try to copy/paste the "bin" and "chapters" folders from the full version and run the demo to see if the game works that way.
I'll try to upload everything with itch's app to see if that makes installing any easier.

I'll try it that way, thanks!