Clouds were crafted in EmberGen (www.jangafx.com) , exported as VDBs then imported & converted to 3D Volume Textures within Unreal
more of my simulation videos here: / jasonkey3d
EmberGen does REAL-TIME VOLUMETRIC FLUID SIMULATIONS FOR GAMES AND FILM
https://jangafx.com/software/embergen/
Follow me here:
/ key_vfx
/ keyjason