How Fog Works
Atmospheric fog softens distant scenery and helps establish depth. Its appearance can vary by biome, weather, dimension, shader and edition. A hazy horizon does not always mean the game has stopped loading chunks at that exact point.
Check Visibility
Test during clear weather from an open viewpoint. Compare the result without optional shaders or visual packs. If terrain is present but fades into the atmosphere, a distance increase alone may not create the look you expect.
Compatibility
Read the documentation for any fog modification and confirm its version compatibility. Removing fog can reveal the terrain boundary more clearly. It does not automatically increase simulation distance or cause a multiplayer server to send more chunks.
Further reading: Minecraft Creator documentation on render and simulation distance. Settings and mod compatibility vary by edition and version.