The folder structure of your files gets lost when you build the game. The StreamingAssets folder is left as-is in your built project, but those files will be accessible and modifiable to users.
I recommend using ScriptableObjects to organize your assets. A ScriptableObject is like a monobehaviour that doesn’t attach to a GameObject or belong to a scene, and sits as an asset in your project folder. You could write a single ScriptableObject class and instantiate multiple copies to represent your different content categories and store references to them. Unity - Manual: ScriptableObject
Here’s an example.
using UnityEngine;
[CreateAssetMenu(fileName = "AssetCategory", menuName = "Data/AssetCategory", order = 0)]
public class AssetCategory : ScriptableObject
{
public Sprite[] spriteAssets;
public AudioClip[] audioAssets;
}
That will add a new “create” option when you right-click in the asset folder.
You can then assign references to your new asset like you could with a monobehaviour.
Objects in your scene can store references to your ScriptableObjects for easy access.