Default Value in Data Validation built off a table and allowing for multiple uses using VBA

Hello,

Another part of a prior project I'm working on: 

There are two cells with two different data validation lists. List A is the primary, list B has several different lists depending on the value of list A. I would like for list B to change to a default value for each of its sub-lists. I have a semi-functional code that has worked a few times but it ends to break down on me, and I'm not sure why.

List B uses an XLookup formula in the data validation field to decide which list is available. My method for getting a default value for this list is by using VBA to change the value of the data validation cell to an xlookup formula that only uses one column of the B sub-lists as the output, making them the "default". This is set up in a way so that ideally it only changes to the default when List A changes value. For other reasons this worksheet also needs to function with automatic calculations. This sheet will also need to be able to update as List A changes value, automatically reselecting the default list B value for each List A value.

Here's the VBA code and an example of an application of the method - not the actual worksheet that needs to work. Just a VBA playground sheet.

Private Sub Worksheet_Change(ByVal Target As Range)
    Application.EnableEvents = False
        With ActiveSheet
            If Not Intersect(Target, Range("F3")) Is Nothing Then
  
                'Action code
                .Range("G3").Formula2 = "=XLOOKUP(F3,testTable[Alphabet],testTable[Item Default])"
    
    
            End If
        End With
    Application.EnableEvents = True
End Sub