Reboot and press F1 to enter the BIOS Setup menu. (Recommended way to enter BIOS for Think Series). Go to Security, select UEFI BIOS Update Option, then select Secure RollBack Prevention and set it to Disabled. Save and Exit. Flash the BIOS again.
Unable-to-Flash-Bios-m92p-Tiny – English Community – LENOVO COMMUNITY
https://blog.entek.org.uk/notes/2022/04/19/updating-lenovo-m72e-tiny-pc-bios.html