Question Missing Assets from detail Mesh

Hello, I am new to Unity's interface and have decided to create a 3D game using this platform as a beginner game developer. I have been watching several YouTube videos and tutorials on how to create and edit terrain, but most of them are brief and don't explain the process or the idea behind how the program works in a proper way for beginners who know nothing at all. It's also difficult to search for specific information in the Unity documentation. While editing the terrain, I've been trying to add terrain detail meshes such as grass and bushes. However, when I try to select a GameObject, only the objects from one asset pack, which is the "Terrain Asset sample pack" by Unity, are shown. I want to add meshes from another asset pack (https://assetstore.unity.com/packages/3d/environments/lowpoly-environment-nature-pack-free-187052), but I'm not sure why I can't find or set the meshes of that other asset pack as detail prefabs so that I can paint them on my terrain. I'm not sure if this has anything to do with the built-in Unity Terrain Tools or with the URP or HDRP settings. How can I know what my Unity is set to? I apologize for the lengthy question, but every time I try to start in game development, I get demotivated due to similar problems with no easy explanations for people with no experience.

I have included a screenshot of my user interface as an additional resource to potentially assist in identifying the issue. I will be grateful any assistance provided.

 

You cannot „paint“ skyboxes. A skybox is a separate feature that uses a separate workflow, it is not a mesh or something you paint on terrain. I believe it is set up through Lighting settings but I‘m recalling that from memory.

 

Hello, I am sorry about the confusion I have mixed up the asset packs I meant to link different one which is the low poly environment pack (https://assetstore.unity.com/packages/3d/environments/lowpoly-environment-nature-pack-free-187052). It contains a couple of meshes but I am usable to use/find them in the mesh detail menu.