How to programmatically set Excel Sensitivity Labels using C#, Microsoft.Interop.Excel?

Question

Our IT department applied a policy where we have to specify Sensitivity Label in Excel. I have successfully been able to do this in VBA. Does anyone know how to in c#, microsoft.interop.excel?

code for vba below

    Dim lblInfo As Office.LabelInfo
    Dim noSenseLabel As SensitivityLabel
    Set xlSQL = CreateObject("Excel.Application")
    xlSQL.Visible = False
    'xlSQL.Visible = True
    
    If xlSQS Is Nothing Then
        Set xlSQS = xlSQL.Workbooks.Add
        Set noSenseLabel = xlSQS.SensitivityLabel
        Set lblInfo = noSenseLabel.CreateLabelInfo()
        
        With lblInfo
            .AssignmentMethod = MsoAssignmentMethod.PRIVILEGED
            .LabelId = "9203368f-916c-4d59-8292-9f1c6a1e8f39"
            .LabelName = "MyLabelName"
            .SiteId = "6c15903a-880e-4e17-818a-6cb4f7935615"
        End With
        
        noSenseLabel.SetLabel lblInfo, lblInfo
        
        xlSQS.SaveAs xlFn, 51
    
        'Set noSenseLabel = xlSQS.SensitivityLabel
        'Set lblInfo = noSenseLabel.GetLabel()
        'Debug.Print lblInfo.LabelId
        'Debug.Print lblInfo.LabelName
        'Debug.Print lblInfo.SiteId
    
    Else
    End If

Answer 1

I found out how to do it. From my testing it doesn't work on .NET Framework (even 4.8.1), I tried on .NET 6.0 and it works out of the box.

Create a new Console application based on .NET 6.0, add a COM reference to Microsoft Office Excel 16 Object Library (if O365 is installed on our system you should just find it under the COM list).
Write your code (basically converting your VBA), start with something simple as:

using Excel = Microsoft.Office.Interop.Excel  

then:

Excel.Application exApp = new Excel.Application();
Excel.Workbook wb = exApp.Workbooks.Add();
var label = wb.SensitivityLabel;

You should get intellisense while writing SensitivityLabel and see a squiggly red line under it telling you that you need to reference something like office, 15.0.0.0, ignore that and add another COM reference: Microsoft Office 16 Object Library.
The squiggly red line will still be there, build the project and after that everything will be fine.

Unfortunately I was not able to find a reliable way for .NET Framework.