Wow, I honestly have never seen that before, Windows 11 installed on a Legacy Boot device, and that is causing the problem
Secure Boot will not work on Legacy BIOS and that is the main cause of your problem, and to convert your system to UEFI BIOS is a big job, the first thing is the drive would need to be converted to a GPT partition style, then your BIOS needs to be switched to UEFI
There are two methods to convert the drive.
1
Backup your personal files, then clean install Windows 10 form a bootable USB and before doing that you will need to change BIOS to UEFI and convert the drive form MBR to GPT, which would wipe all data on the drive.
2
You can try to convert the drive without data loss from MBR to GPT using the tool that Microsoft provide, then boot into BIOS and switch to UEFI Mode
Before you attempt to do this, please backup your personal files.