I'm getting a different error in .NET 8.0. Here is my code:

Microsoft.Office.Interop.Excel.Application xl = new();

Workbook wb = xl.Workbooks.Open(filepath);

dynamic noSenseLabel = xl.ActiveWorkbook.SensitivityLabel;

dynamic lblInfo = noSenseLabel.CreateLabelInfo();

lblInfo.LabelId = labelId;

lblInfo.LabelName = "Sensitive";

lblInfo.SiteId = siteId;

noSenseLabel.SetLabel(lblInfo, lblInfo);