You can mix the 2 by custom shader and ray marching.
You just need to calculate the light level of each specific pixel. Based on ray penetration into a volume.
For older gfx that’s hell - so you fall back to a sprite.
For newer cards, this is trivial. Even a 3060 has enough overhead to calculate each pixel on a 4k screen several times over before rendering…
What would be most helpful, is a system to draw up clouds in engine and render the final sprite as a finalized 2d transparent PNG.
Obviously that will lock in the light vector to a specific coordinate.
At which point for older cards you could loop several images based on the light vector incidence.
Mind you, this is pure theory at the moment.
Achievable outside the engine though.