Thank you for contacting Aspose support.
There could be a difference in how you are trying to achieve your goal, therefore please review the below provided code snippet & attached output file for your reference.
Workbook book = new Workbook();
Worksheet sheet = book.getWorksheets().get(0);
Cell A1 = sheet.getCells().get(“A1”);
A1.putValue(“This is a very very long text”);
int styleIndex = book.getStyles().add();
Style style = book.getStyles().get(styleIndex);
StyleFlag flag = new StyleFlag();
book.save(myDir + “output.xlsx”);
Please feel free to write back in case you face any difficulty.