exhibit321_2024section90

Exhibit 32.1 Certification by the Chief Executive Officer Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 In connection with the Annual Report of Constellium SE (the “Company”) on Form 10-K for the year ended December 31, 2024 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Jean-Marc Germain, Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to my knowledge: (1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and (2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company. Date: February 28, 2025 By: /s/ Jean-Marc Germain Name: Jean-Marc Germain Title: Chief Executive Officer