Thanks a lot! I will look into this.
I have created this bug ticket and you can track it here:
https://trello.com/c/PTDqreRn/29-black-screen-when-playing-on-itchio-app-and-var...
I was able to reproduce the issue on my computer as well. I tried everything but I am getting a bit desparate. I have now asked Reddit for help: https://www.reddit.com/r/godot/comments/k8oefc/my_game_does_not_load_in_the_itch... let's see if this leads to anything...
EDIT
After many hours of research I discovered this bug on the itch app: https://github.com/itchio/itch/issues/2496
and I can confirm that in the beta version of the next release the issue is gone. Looks like we have to wait!