I followed a GreenLuma tutorial to unlock DLCs for a few single-player games on Steam. The step-by-step guide I found was surprisingly detailed—covering everything from downloading the right GreenLuma files to configuring bin files and using appid lists.
This is the most important chapter of this GreenLuma tutorial. greenluma tutorial
You must already have the game files. GreenLuma does not download games for you; it only unlocks the license to run them. I followed a GreenLuma tutorial to unlock DLCs