Private Sub CommandButton1_Click()
    Dim r As Range
    Dim rng As Range
    Dim intI As Integer
    Dim intCount As Integer

    TextBox1.Text = ""

    If ComboBox1.ListIndex = - 1  Then Exit Sub
    
    Set rng = ThisWorkbook.Worksheets("Лист1").Range("A1:A20")
    
    ' Поиск совпадений.
    For Each r In rng.Cells
        If ComboBox1.List(ComboBox1.ListIndex) = r.Value Then
            intCount = intCount +  1 
        End If
    Next r
    
    TextBox1.Text = intCount
End Sub

Private Sub CommandButton1_Click()
    Dim r As Range
    Dim rng As Range
    Dim intI As Integer
    Dim blnFlag As Boolean
    
    Set rng = ThisWorkbook.Worksheets("Лист1").Range("A1:A11")
    
    For Each r In rng.Cells
        blnFlag = False
        
        If ComboBox1.ListCount =  0  Then
            ComboBox1.AddItem r.Value
        Else
            For intI =  0  To ComboBox1.ListCount -  1 
                If CLng(r.Value) = CLng(ComboBox1.List(intI)) Then
                    blnFlag = True
                    Exit For
                End If
            Next intI
            
            If Not blnFlag Then
                ComboBox1.AddItem r.Value
            End If
        End If
    Next r
End Sub

    If ComboBox1.List(ComboBox1.ListIndex) = r.Value Then
        intCount = intCount +  1 
    End If

    If CLng(ComboBox1.List(ComboBox1.ListIndex)) = CLng(r.Value) Then
        intCount = intCount +  1 
    End If

?UCase("макрос")=UCase("маКрос")
True

' Или.

?LCase("макрос")=LCase("маКрос")
True

    If CLng(r.Value) = CLng(ComboBox1.List(intI)) Then
        blnFlag = True
        Exit For
    End If