Hey, no sorry. The clould shadows were created with the built in Hard Drop Shadow shader in Gamemaker Studio 2. I made a note of that above in the description above.
You might already know this but just in case: A quick way to get shadows is by turning the clouds tileset into a shadow version of itself. You can very quickly do that by darkening the entire cloud tileset to black and then dropping the opacity to something like 25%, or to what suits your game.