It helps to have some sort of visual cue in the playspace that extends into the background. So if the player is standing next to a tree, and you see the same type of trees in the distance, your brain sort of plays a trick on itself, and says “Oh, that’s far away and really epic!”
A lot of artists use VUE and PS to make their skies
GAEA Quadspinner
Nuke is mentioned for 32bit (hdr) compositing of matte paintings
Put clouds on an animated spline
You can create large hero clouds, you can stack textures on a rectangular texture, you can pack textures into the RGB channels. There are so many ways to make cloud textures that it really comes down to preference, and performance. You can then paint in rim light control and add movement in the shader in Unreal
https://www.youtube.com/watch?v=hUsTVBbp7hc Tu Bui outdoor lighting fundamentals
https://www.youtube.com/watch?v=UNokcDYiLiA&list=RDCMUCat3IRxZSuUyxm_dnCWJQyA&index=2 Maxx Burman matte painting video
I own the super cool Tyler Smith cloud tutorial that I can follow.
https://80.lv/articles/creating-breathtaking-game-backgrounds/ this article also has a Photoshop trick explained for cloud cards.
Get a Blender workflow going with the right plugins and tools to generate landscapes
https://youtu.be/Se4e2DQ_D5g anything from here really
https://youtu.be/yrMee2gcS20 completely vanilla Blender tutorial on making a large scale landscape
https://youtu.be/paDzvhHk3iE bagapie addon with scattering
Find a way to create good looking normals from cloud mattes
Use/make alpha trees for faster rendering times