This is the most reliable "library" for older software. Search for "Windows 7 Professional SP1 64-bit" or "Windows 7 Ultimate SP1 64-bit." Look for "Official ISO" or "Retail" uploads that match the version you have a license for. Third-Party Downloader Tools:

This means the ISO lacks the correct bootmgfw.efi . Rebuild the USB using Rufus in DD Image Mode (Rufus will ask you when writing). Also, ensure CSM is enabled.