There is not really a need/use for a custom editor here.
The "issue" is that properties are not serialized by Unity. So a custom editor wouldn't help much. Even if you somehow manage to expose such a field in the Inspector any changes in it wouldn't get stored anyway
All you need actually would be a serialzed backing field like
[Serializable]
public class SomeClass
{
public int someUnneededVariable;
// You probably wouldn't need the setter anyway
public UnityEvent someEvent { get => _someEvent; set => _someEvent = value; }
[SerializeField] private UnityEvent _someEvent;
}
[Serializable]
public class MyChild : SomeClass
{
}
Or if you already have a custom editor for the parent type you could simply make sure that you pass in true in CustomEditor
editorForChildClasses
If true, child classes of inspectedType will also show this editor. Defaults to false.