Hi Marcus,
Thank you very much for your interest in Syncfusion Products.
Essential XlsIO can hide the text box border by using the IShapeLineFormat interface, which is used to modify the border. So, to hide the border of the text box, you can use the below code snippet. Please try this at your end and let us know if this helps you.
[C#]
ITextBoxShape textBox = workbook.Worksheets[0].TextBoxes.AddTextBox(2, 2, 25, 100);
textBox.Line.Visible = false;
To know more about the text box, please navigate to the below link and refer the documentation.
http://help.syncfusion.com/ug_91/Reporting/XlsIO/Windows%20Forms/default.htm?turl=Documents%2Ftextbox.htmPlease let us know if you need any further assistance.
Regards,
Pauline Bosco.