Past 200 studs the terrain rendering gets worse and worse, this happens both in studio and in game on max graphics.
Turn on streaming enabled to not even render that area.
Is your studio settings Render settings all on Automatic?
Hello, It seems to me that streaming enabled isn’t turned on for you, for more on this please feel free to read upon the source that is provided for you here. →
Content Streaming | Roblox Creator Documentation
The terrain rendering gets worse the farther you look out to improve rendering performance (this is called Level of Detail, LOD for short) so unfortunately this isn’t something you can disable. You can try covering up Terrain LOD by using Fog settings in Lighting or with an atmosphere object under lighting.