You need to create a bootable Windows 10 USB drive and then replace the install.wim file in the ‘sources’ folder in Windows 10 USB with the install.wim file from Windows 11 ISO image.
src - https://allthings.how/how-to-install-windows-11-on-legacy-bios-without-secure-boot-or-tpm-2-0/
src - https://allthings.how/how-to-install-windows-11-on-legacy-bios-without-secure-boot-or-tpm-2-0/