It is an issue with the distribution you're trying to install having an entry in the exclusion (not allowed) database.  The  technical details are linked below. [URL]  
I am trying to boot into Arch Linux live with a secure boot enabled USB. I am getting this error: OS Loader signature found in Secure boot exclusion database (dbx). Bootable device failed Secure  boot verification. Is Windows 11 or the Dell BIOS updates blacklisting the Linux to boot?
Bootable USB : Bootable device failed Secure  boot verification.