2020.1.14f1

[AldeRoberge]

Is it supposed to work for Unity 2020?

This is what I get.

[ATHellboy]

Hey @AldeRoberge,

It works on Unity 2020.1.15. So I think, there isn't any problems with Unity 2020.1.14 either.
Please check out Usage Example.

I think, that happens because of not using ScriptableObjectReference class.

using UnityEngine;

[CreateAssetMenu(menuName = "Create Block")]
public class Block : ScriptableObject
{
    // Some fields
}

using ScriptableObjectDropdown;
using UnityEngine;

public class BlockManager : MonoBehaviour
{
    // Without grouping (default is None)
    [ScriptableObjectDropdown(typeof(Block))] public ScriptableObjectReference targetBlock;
    // By grouping
    [ScriptableObjectDropdown(typeof(Block), grouping = ScriptableObjectGrouping.ByFolder)]
    public ScriptableObjectReference targetBlockByGrouping;
}