Not the best soloutin but you can Create Child of the game Object which you want it to have drop shadow , let the child gameObject have the same sprite as the parent and change it color to black (or the color you want to use as shadow)
And set it layer to a layer lesser than the parent object and adjust it position to what you like
There's other soloutins in youtube , which create a script that automaticlly create the child game object(the drop shadow) for you