kuligs2 By the looks of it, Sable does it with a plain environment texture. If you want the coolest (and still simple) way that lets you animate/morph cloud shapes, best to do it with procedural 3d noise sky shader. Although for that thin outline an additional post processing shader would be needed.
Start with a prerendered environment. If that is not "cool" enough in the context of the whole game, then start thinking about procedural sky.
Godot's skies use equirectangular 360 deg textures. You can render them out of any decent 3D program. There are also online converters from standard cubemaps to equirects. You're likely using Blender. Cycles can directly render out full equirect environments.
If you plug a prerendered texture into a sky shader, you can still animate it in a nice looking way by perturbating sampling coordinates (per pixel) and rotating the environment. You can also composite several such textures in the shader, each having different rotation speed and perturbation amplitude/period.