I created this cinematic environment in Unreal Engine 5. I got inspiration from Shangrila Resort in Pakistan. I combined two different weather situations here. Environment is lit by Lumen and reflections are Raytraced. Let me explain a process, I created the back mountains in World Creator and exported the height map in the engine. New modeling Tools are totally GAME CHANGER! I didn't use the height map in Landscape Mode of unreal, but I created static meshes using Displace Option in modeling tools. You can directly create static meshes of mountains or anything in Unreal Engine and also can optimize them.
First create blank plane, Remesh it to target polygons- Displace 2D Texture Map - Simplify/Decimate
No need of any other DCC app or to go outside the unreal for this. You should definitely give a try to these new modeling tools.