Hi please try following examples
---EXAMPLE #1 - Sheet is hidden ---
Workbook wb = new Workbook();
wb.Worksheets.Clear();
wb.Worksheets.Add("Another Sheet");
Worksheet ws = wb.Worksheets.Add("New");
ws.IsVisible = false;
wb.Save(@"Result.xlsx", FileFormatType.Excel2007Xlsx);
---EXAMPLE #1 END ---
---EXAMPLE #2 - Sheet is not hidden ---
Workbook wb = new Workbook();
wb.Worksheets.Clear();
Worksheet ws = wb.Worksheets.Add("New");
ws.IsVisible = false;
wb.Worksheets.Add("Another Sheet");
wb.Save(@"Result.xlsx", FileFormatType.Excel2007Xlsx);
---EXAMPLE #2 END ---