Washington, D.C. 20549 As filed with the Securities and Exchange Commission on October 30, 2025. Registration No. 333-280398 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Post-Effective Amendment No. 2 to FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 FLAGSTAR BANK, NATIONAL ASSOCIATION United States of America (State or Other Jurisdiction of Incorporation or Organization) 6036 (Primary Standard Industrial Classification Code Number) 38-2734984 (I.R.S. Employer Identification No.) 102 D ...