Hello, Thank you for letting us know about this issue. We've determined that the game is only displaying this error when you download the Mac OS version as a zip from Itch and unfortunately it's a known Unity issue. If you download the game via the Itch launcher or via Steam you shouldn't have this issue.
If you still want to download the game as a zip, you'll need to take some additional steps.
First, you can try moving the game to your Applications directory, ctrl + clicking, and selecting "Open."
In the event that this does not resolve the issue, you can take these more technical steps:
CTRL + Click on NotItSE.app
Click New Terminal at Folder
Type xattr -rc .
Then you should be able to open the game.