Yes, it is cuttable. Please refer to page 33 of the Stainless Steel Flue Fittings guide: https://www.reznor.co.uk/wp-content/uploads/2023/12/Reznor-Dimensional-Data-Sheet-Stainless-Steel-Flue-Fittings-EN-2021-12-D301382-Issue-0.pdf.
Is the warm air flue cuttable?
Information about Reznor's range of flue