You have to add a bit more code, specifically you must give the grid a list of properties explicitly, deriving from PropertyDescriptor, something like this:

public class CustomType : DynamicObject, ICustomTypeDescriptor
{
    private readonly Dictionary<string, object> _properties = new Dictionary<string, object>();

    public AttributeCollection GetAttributes() => new AttributeCollection();
    public string GetClassName() => null;
    public string GetComponentName() => null;
    public TypeConverter GetConverter() => null;
    public EventDescriptor GetDefaultEvent() => null;
    public PropertyDescriptor GetDefaultProperty() => null;
    public object GetEditor(Type editorBaseType) => null;
    public EventDescriptorCollection GetEvents() => GetEvents(null);
    public EventDescriptorCollection GetEvents(Attribute[] attributes) => new EventDescriptorCollection(null);
    public PropertyDescriptorCollection GetProperties() => GetProperties(null);
    public object GetPropertyOwner(PropertyDescriptor pd) => this;
    public PropertyDescriptorCollection GetProperties(Attribute[] attributes) => new PropertyDescriptorCollection(_properties.Select(p => new CustomProperty(p.Key, p.Value, "Mycats")).ToArray());

    public override bool TryGetMember(GetMemberBinder binder, out object value) => _properties.TryGetValue(binder.Name, out value);
    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        _properties[binder.Name] = value;
        return true;
    }
}

public class CustomProperty : PropertyDescriptor
{
    public CustomProperty(string name, object value, string category)
        : base(name, new Attribute[] { new CategoryAttribute(category) })
    {
        Value = value;
    }

    public object Value { get; set; }
    public override Type ComponentType => typeof(CustomType);
    public override bool IsReadOnly => false;
    public override Type PropertyType => Value != null ? Value.GetType() : typeof(object);
    public override bool CanResetValue(object component) => false;
    public override object GetValue(object component) => Value;
    public override void ResetValue(object component) => throw new NotSupportedException();
    public override void SetValue(object component, object value) => Value = value;
    public override bool ShouldSerializeValue(object component) => false;
}