It shouldn't be a macOS issue, as I developed the entire demo and its DLC on a Mac, and they run just fine ^^; Please provide screenshots of how you've tried to install the DLC into the "game" folder so I can get a better understanding of what your issue is.
This is also just a friendly and lighthearted suggestion (one that you're welcome to ignore), but I wouldn't rely on ChatGPT for answers, as it's widely known to spread misinformation, uses stolen data, and is harmful to the environment T_T