I think this is a rare game engine bug that happens on a select few systems. Ideally, restarting the game will do the trick, but as of now there isn't a known fix.
Recent community posts
Make sure the game is extracted before you try to run it. After downloading the file, right-click on it and choose "Extract All..." and follow the prompts. When you're done, there will be a new "ddlc-win" folder alongside the zip file that you downloaded. You can then delete the original zip file and run DDLC from the extracted folder.
It's an issue with Gatekeeper. I've seen success by copying the application out of its folder and putting it directly on the desktop, but if that doesn't work then you may need to look up Gatekeeper disable methods or workarounds.
Thank you for the suggestion. I'll update the content warning page to clarify that DDLC is a horror game. Since the game is already listed as horror on Steam, I'll update the tags on itch.io to include it as well.
Did you ever get any initial error when starting up the game? You have to make sure the game resides in an area that isn't read-only, such as your desktop. I've heard some Mac users were getting read-only related errors, and copying the game to desktop or re-downloading it helped fix the issue.