How can I enable the UEFI/legacy option?
You cannot. Your hardware does not support Compatibility Support Module (CSM). Your device has a 10th generation Intel Core processor, per Intel's announcement in July 2020, your processor was only validated to support UEFI.
Intel previously announced that in 2020 they are phasing out support for legacy Basic Input/Output System (BIOS) boot mode. This means that many of the Lenovo products launching in 2020 will no longer support the Legacy Boot option in BIOS. The only Boot option that will be supported on those products is Unified Extensible Firmware Interface (UEFI).
Source: Legacy BIOS Boot Support Removed in Lenovo 2020 products
Intel Announcement: Legacy BIOS Boot Support Removal for Intel Platforms Technical Advisory
Starting with client platforms launching in 2020. Intel will no longer be supporting legacy Basic Input/output System (BIOS) mode.
- This Includes 10th generation Intel platforms launching in 2020 and all future platforms.