My Dell XPS 8930 is now "upgraded" to Windows 11 (big mistake!).  In the BIOS, I needed to disable secure boot in order to perform a function.  Now I want to re-enable secure boot.

In the BIOS when I try to toggle Secure Boot from disable to enable, I get the following warning message: "Secure Boot is not allowed if the system in legacy boot mode."  The Boot List Option is (and always has been) UEFI.  

How can I re-enable Secure Boot?