a little of both. you can make a second version of your item and make it more high poly then sculpt wrinkles with blender's sculpting mode

then when you bake the texture you use that version so you have all that detail

then you use the lower poly model for your actual clothing you upload, and maybe pull the folds out a little for depth

you can also accent the wrinkles further in your image editing software

ooh thankyou very much!!!. I will try it