There is a Secure Boot Security Vulnerability that has been addressed by Intel CVE-2020-10713. Dell and other OEMs have been releasing a series of UEFI BIOS Updates to patch this.
The Security Update is related to the Grand Unified Bootloader 2 (GRUB2) which most Linux distributions which formerly passed Secure Boot rely on.
If you have an older Linux distribution installed or are using an older installation ISO you will get Verification Failed: (0x1A) Security Violation and either be forced to disable Secure Boot to boot into your old installation to update or begin the install from an older ISO or seek a newer installation ISO.
The Ubuntu 20.04.1 ISO, Ubuntu 20.10 ISO and Linux Mint 20.1 ISO have been updated to pass Secure Boot.
Fedora 33 and DeepIn 20.1 which previously passed Secure Boot are now rejected by Secure Boot.