OK, you might still be able to get it to work. In your Steam library, right click on Our Life and go to the "Manage" section of the drop down. From there click "Browse Local Files". You're looking for the DLC files, which in Windows are under "Game", and should be the same on Mac. The files you're looking for are called "dlc_step_1.rpa", or whatever DLC you have. You should be able to copy those files directly out of that folder and put them in the "game" folder of the itch.io version you can download for free. Hopefully that works! Otherwise, let me know. And thank you so much for playing.