A Dictionary that automatically resizes to the size of the enum in its definition, that is serialized with Unity. Along with it's drawer for the Unity Editor.

EnumDictionary.cs

using System;
using UnityEngine;

namespace EnumDictionaries
{
    public abstract class EnumDictionaryBase
    {
    }

    [Serializable]
    public class EnumDictionary<TKey,TValue> : EnumDictionaryBase, ISerializationCallbackReceiver where TKey : Enum
    {
        [SerializeField] public TValue[] Values;

        public TKey EnumType = (TKey)(object)0;

        public TValue this[TKey button] => Values[(int)(object)button];

        public void OnBeforeSerialize()
        {
            
        }

        public void OnAfterDeserialize()
        {
            var keys = (TKey[])Enum.GetValues(typeof(TKey));
            if(Values == null) Values = new TValue[keys.Length];
            
            if (keys.Length > Values.Length)
            {
                var newValues = new TValue[keys.Length];
                for (int i = 0; i < Values.Length; i++)
                {
                    newValues[i] = Values[i];
                }

                Values = newValues;
            }

        }

    }
}

EnumDictionaryDrawer.cs

using System.Collections.Generic;
using EnumDictionaries;
using UnityEditor;
using UnityEngine;

namespace Editor.EnumDictionary
{
    [CustomPropertyDrawer(typeof(EnumDictionaryBase), true)]
    public class EnumDictionaryDrawer : PropertyDrawer
    {
        private const string ValuesFieldName = "Values";
        private const string EnumTypeFieldName = "EnumType";

        private bool _isFoldout = true;

        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        {
            var valueArrayProperty = property.FindPropertyRelative(ValuesFieldName);
            var enumNames = property.FindPropertyRelative(EnumTypeFieldName).enumDisplayNames;

            position.height = EditorGUIUtility.singleLineHeight;
            _isFoldout = EditorGUI.Foldout(position,_isFoldout,label);
            position.y += EditorGUIUtility.singleLineHeight;

            if (_isFoldout)
            {
                EditorGUI.indentLevel++;
                DrawElements(ref position, valueArrayProperty, enumNames);
                EditorGUI.indentLevel--;
            }
        }

        public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
        {
            var height = EditorGUIUtility.singleLineHeight;

            if (_isFoldout)
            {
                var arrayProperty = property.FindPropertyRelative(ValuesFieldName);
                var arraySize = arrayProperty.arraySize;
                for (int i = 0; i < arraySize; i++)
                {
                    var elementProperty = arrayProperty.GetArrayElementAtIndex(i);
                    height += EditorGUI.GetPropertyHeight(elementProperty) + EditorGUIUtility.standardVerticalSpacing;
                }
            }

            return height;
        }


        private void DrawElements(ref Rect position, SerializedProperty arrayProperty, string[] enumNames)
        {
            var arraySize = arrayProperty.arraySize;
            for (int i = 0; i < arraySize; i++)
            {
                var elementProperty = arrayProperty.GetArrayElementAtIndex(i);
                var elementHeight = EditorGUI.GetPropertyHeight(elementProperty);
                position.height = elementHeight;
                EditorGUI.PropertyField(position, elementProperty, new GUIContent(enumNames[i]), true);
                position.y += elementHeight  + EditorGUIUtility.standardVerticalSpacing;

            }
        }
    }
}