Workbook_open not firing due to compile error in class module (missing library reference)

Hi all,
after hours of research in the web I finally need to ask here for your help: Following problem: I try to add a reference (Outlook library) in the Private Sub Workbook_Open() event (yes, it's in ThisWorkbook) since I need early binding for getting Outlook events later in different places. Once I open my workbook I get a compile error "user-defined type not defined" in my class module here --> Private olApp As New Outlook.Application. I understand this since the Outlook reference is not yet set and this is what I exactly try to do in the Workbook_Open event. How does Excel work here? Does it first try to compile the project BEFORE it executes code in the Workbook_Open event (enableEvents is set to True)?
Once I run the Sub Workbook_open manually, the reference is set without any problems.
Thanks in advance for your help.

Trying to add reference for MS Outlook Object Library when Workbook opens:

Private Sub Workbook_Open()
    Dim strGUID As String, theRef As Variant, i As Long
'Update the GUID you need below.
    strGUID = "{00062FFF-0000-0000-C000-000000000046}" 'MS Outlook x.x Object Library

'Set to continue in case of error
    On Error Resume Next

'Remove any missing references
    For i = thisWorkbook.VBProject.References.Count To 1 Step -1
        Set theRef = thisWorkbook.VBProject.References.Item(i)
        If theRef.isbroken = True Then
            thisWorkbook.VBProject.References.Remove theRef
        End If
    Next i

'Clear any errors so that error trapping for GUID additions can be evaluated
    Err.Clear

'Add the reference
    thisWorkbook.VBProject.References.AddFromGuid _
    GUID:=strGUID, Major:=1, Minor:=0

'If an error was encountered, inform the user
    Select Case Err.Number
    Case Is = 32813
         'Reference already in use.  No action necessary
         MsgBox "Reference already in use"
    Case Is = vbNullString
         'Reference added without issue
         MsgBox "Reference added"
    Case Else
         'An unknown error was encountered, so alert the user
        MsgBox "A problem was encountered trying to" & vbNewLine _
        & "add or remove a reference in this file" & vbNewLine & "Please check the " _
        & "references in your VBA project!", vbCritical + vbOKOnly, "Error!"
    End Select
    On Error GoTo 0
End Sub

Here the Class Module "ClsAppoint" in which the compile error occurs once I open the workbook (red line):

Option Explicit
Private olApp As New Outlook.Application 
Public WithEvents Appoint As Outlook.AppointmentItem
Private invite_sent As Boolean

Private Sub Class_Initialize()
    Set Appoint = olApp.CreateItem(olAppointmentItem)
    invite_sent = False
End Sub

Private Sub Appoint_Close(Cancel As Boolean)
    Dim CloseAndDiscard As VbMsgBoxResult
    If invite_sent Then Exit Sub
    Appoint.GetInspector.WindowState = olMinimized
    AppActivate Application.Caption
    
    CloseAndDiscard = MsgBox("Close and discard?", vbYesNo + vbQuestion)
    
    If CloseAndDiscard = vbYes Then
        Appoint.Close olDiscard
        Set invite = Nothing
    Else
        Cancel = True
        Appoint.Display
        Exit Sub
    End If
    
End Sub

Private Sub Appoint_Send(Cancel As Boolean)
    invite_sent = True
    invite.Appoint.SaveAs save_email_folder & invite_name
    Set invite = Nothing
End Sub