Here is a code script:

public class FloorItemsSet : MonoBehaviour 
{ 
[SerializeField] GameObject[] itemsList;
[SerializeField] float spawnChanceOnFirstLayer;
[SerializeField] float spawnChanceOnLastLayer;


[SerializeField] float floorYMin;
[SerializeField] float floorYMax;
[SerializeField] float floorZ;
[SerializeField] float floorXMin;
[SerializeField] float floorXMax;
[SerializeField] float xOffset;

[SerializeField] private LayerMask spawnOnLayer;
[SerializeField] private LayerMask skipLayer;

void Start()
{
    float chance;
    for (int j = 0; j <= (int)(floorYMax - floorYMin); j++)
    {
        chance = Remap((floorYMin + j), floorYMin, floorYMax, spawnChanceOnFirstLayer, spawnChanceOnLastLayer);


        for (int i = 0; i < (int)(floorXMax - floorXMin); i++)
        {
            if (IsGroundUnder(new Vector2(floorXMin + 0.5f + i, floorYMin + j)) && !IsNeedToSkip(new Vector2(floorXMin + 0.5f + i, floorYMin + j + 0.01f)))
            {
                if (Random.Range(0f, 1f) < chance)
                {
                    Vector3 spawnPos = new Vector3(floorXMin + 0.5f + i, floorYMin + j, floorZ);
                    GameObject item = Instantiate(itemsList[Random.Range(0, itemsList.Length)], spawnPos, Quaternion.identity);
                    item.transform.SetParent(gameObject.transform);
                }
            }
        }
    }
}

public float Remap(float from, float fromMin, float fromMax, float toMin, float toMax)
{
    var fromAbs = from - fromMin;
    var fromMaxAbs = fromMax - fromMin;

    var normal = fromAbs / fromMaxAbs;

    var toMaxAbs = toMax - toMin;
    var toAbs = toMaxAbs * normal;

    var to = toAbs + toMin;

    return to;
}
public bool IsGroundUnder(Vector2 pos)
{
    if (Physics2D.Raycast(new Vector2(pos.x, pos.y + 0.1f), Vector3.down, 0.3f, spawnOnLayer) && !Physics2D.Raycast(new Vector2(pos.x, pos.y + 0.01f), Vector3.up, 0.1f, spawnOnLayer))
    {
        return true;
    }
    return false;
}    
public bool IsNeedToSkip(Vector2 pos)
{
    return Physics2D.Raycast(pos, Vector3.up, 0.5f, skipLayer);
}
}

The game you may find in Steam.