I have several forms and several TextBoxes in each form. To isolate the code I use a class CCtrlTextBoxEvent
enabling events: Public WithEvents txtbox As MSForms.TextBox and i get callbacks on txtbox_Change().

‘Each Form implements IForm which basically has one declaration:

Public Function ChangeStatus(bSet As Boolean, iBit As Integer) As Boolean

'My Form has following code at the start:
Implements IForms

'If changes has been done, save it for enabling buttons
Private bDirty As Boolean
Private txtBoxes() As ICtrlEvent
Private glBWFieldsChanged As Integer

'Callback function to enable/disable controls in form
'Common function to set or clear a bit dependent on the bSet condition
Public Function IForms_ChangeStatus(bSet As Boolean, iBit As Integer) As Boolean
  If bSet Then
    Call SetBit(glBWFieldsChanged, iBit)
  Else
    Call ClearBit(glBWFieldsChanged, iBit)
  End If
  bDirty = glBWFieldsChanged > 0
  EnableButtons
End Function

UserForm_Initialize() 'i set up this structure:
  ReDim txtBoxes(bwiAcDoStart To bwiAcDoEnd)
  
  'Textboxes has to start with 'TB' and comboboxes has to start with 'Cbo'
  'Setup textbox Tb_AccDocDate
  Set txtBoxes(bwiAcDoDate) = GetCtrlClass("Tb_AccDocDate")
  Call txtBoxes(bwiAcDoDate).Init(Me, GetControl("Tb_AccDocDate"), bwiAcDoDate, "Date")
  ...
End Sub

Public Function GetCtrlClass(sCtrlName As String) As ICtrlEvent
  ... error handling
  If Left(sCtrlName, 2) = "Tb" Then
    Set GetCtrlClass = New CCtrlTextBoxEvent
  ElseIf Left(sCtrlName, 3) = "Cbo" Then
    Set GetCtrlClass = New CCtrlComboEvent
  Else
    MsgBox ("GetCtrlClass, unknown ctrl type '" & sCtrlName & "'")
  End If
  ... error handling
End Function

-

—

new class
Class CCtrlTextBoxEvent:

Implements ICtrlEvent

Public WithEvents txtbox As MSForms.TextBox

Private usrForm As IForms
Private referenceString As String
Private bitwCtrl As Integer
Private ctrlType As ICtrlType
Public Sub ICtrlEvent_Init(ByRef uf As IForms, ByRef ctrl As Control, bitw As Integer, sCtrlType As String)
  Set usrForm = uf
  Set txtbox = ctrl
  bitwCtrl = bitw
  referenceString = ""
'  Set ctrlType = GetCtrlTypeClass(sCtrlType)
'  ctrlType.Init (ctrl)
End Sub

‘If New item is loaded, the text will be changed, this is the right entry

Public Sub ICtrlEvent_SetReference(refStr As String)
  referenceString = refStr
End Sub

Private Sub txtbox_Change()
  Call usrForm.ChangeStatus(txtbox.Value <> referenceString, bitwCtrl)
End Sub

So far everything works fine.
Give the control in as a parameter to ICtrlEvent_Init(…) and setup a callback
I get the callback and ChangeStatus get called and no problem

The text boxes in Forms should have different Types like: String, Date, Long, Currency…
What i wanted was to have sub classes for each type, testing on format and if it has valid content.
Implementing a ICtrlType interface and GetCtrlTypeClass to create sub classes CTypeStr, CTypeLong, CType Date and CTypeCurrency. implementing this interface.

First i included extra functions in CCtrlTextBoxEvent
Could probably been properties

Public Function ICtrlEvent_GetValue() As Variant
  If Not ctrlType Is Nothing Then
    ICtrlEvent_GetValue = ctrlType.GetValue
  End If
End Function

Public Function ICtrlEvent_SetValue(ByVal vNewValue As Variant)
  If Not ctrlType Is Nothing Then
    ctrlType.SetValue (vNewValue)
  End If
End Function

Public Function ICtrlEvent_IsValid() As Boolean
  If Not ctrlType Is Nothing Then
    ICtrlEvent_IsValid = ctrlType.IsValid
  End If
End Function

In the CCtrlTextBoxEvent, function ICtrlEvent_Init(…)
I have comented out two lines of code, because its where my problem is

'  Set ctrlType = GetCtrlTypeClass(sCtrlType)
'  ctrlType.Init (ctrl)

Public Function GetCtrlTypeClass(sCtrlType As String)
  ...
  If sCtrlType = "Combo" Then
    Set GetCtrlTypeClass = New CTypeCombo
  ElseIf sCtrlType = "Cur" Then
    Set GetCtrlTypeClass = New CTypeCurrency
  ElseIf sCtrlType = "Date" Then
    Set GetCtrlTypeClass = New CTypeDate
  ElseIf sCtrlType = "Long" Then
    Set GetCtrlTypeClass = New CTypeLong
  ElseIf sCtrlType = "Str" Then
    Set GetCtrlTypeClass = New CTypeStr
  Else
    MsgBox ("GetCtrlTypeClass, unknown ctrl type '" & sCtrlType & "'")
  End If
  ...
End Function

class CTypeDate :

Implements ICtrlType

Dim og_ctrl As MSForms.TextBox

Public Function ICtrlType_Init(ByRef cCtrl As Control) As Boolean
  Set og_ctrl = cCtrl
End Function

Public Function ICtrlType_GetValue() As Variant
  ...
End Function

Public Function ICtrlType_SetValue(ByVal vNewValue As Variant)
  ...
End Function

Public Function ICtrlType_IsValid() As Boolean
  ...
End Function

You see its easy to find the control and set it in the class CCtrlTextBoxEvent
to do: Set txtbox = ctrl -> defined like Public WithEvents og_ctrl As MSForms.TextBox

but trying to call:
ctrlType.Init (ctrl) fails and get a error 424 at runtime.

I can se in documentation, but i dont know how to fix it :
You referred to an object property or method, but didn’t provide a valid object qualifier. Specify an object qualifier if you didn’t provide one. For example, although you can omit an object qualifier when referencing a form property from within the form’s own module, you must explicitly specify the qualifier when referencing the property from a standard module.

Can anyone help me

I tried to set a variable Public WithEvents txtbox As MSForms.TextBox
in a subclass using ctrlType.Init(txtbox) to following class starting with

Implements ICtrlType

Dim og_ctrl As MSForms.TextBox

Public Function ICtrlType_Init(ByRef cCtrl As Control) As Boolean
Set og_ctrl = cCtrl
End Function

Everything compiles, its during runtime I get the error 424