I'm unsure... is there a special link to buy the DLC or is that contained in the main game and I buy that one for whatever I find appropriate?
Viewing post in DLC and macOS version NOW AVAILABLE! comments
The DLC is a separate package from the main game, but everything can be found in the same page when you click the "download" button. Once you choose how much you want to pay for the DLC, you'll be sent to the actual download page, where you will find all the different files for download available in the same place: windows, linux, mac, and the DLC.