This is a paid asset, but now you can download Low Poly Terrain Pack for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Low Poly Terrain Pack v1.0
This pack contains many high-quality low-poly terrains ready to be used in your game to create unique landscapes.
Just drag and drop prefabs to your scene and achieve beautiful results.
All assets are created in a low poly art style, which actually doesn’t require any textures.
The material setups are simple and you are able to customize them easily!
Features:
The package contains 25 Models.
The pack works in HDRP, URP, and Built-in render pipeline.
This pack comes with an extended commercial license, which means you can use these effects to create stunning designs for yourself and your clients!