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 has been updated to address this, the older Ubuntu 20.04 ISO will be rejected. Ubuntu 20.10 also will pass Secure Boot.
Currently Mint 20, Fedora 33, DeepIn 20 (1003) which previously passed Secure Boot are now rejected by Secure Boot.