In 1.16, you could create fog using a texture pack. 

The shaders folder could house a post and program folder.

The program folder, held a file called depth test. 

With this file, I could have fog in Minecraft as shown. 

When a glowing end crystal was in the world, the game would display a fog with the color of your choice.

This is no longer possible for some reason. If you know any fixes, have any information at all,  contact me.

But really, this should be a feature to begin with. A simple /fog command should have been in the game ages ago! I have no idea where the files for this trick came from, and all attempts to find it have proven pointless.