Latitude 7400 - BIOS 1.13.0 - No bootable devices found

Hello,

I have just bought a Latitude 7400. It had Windows 10 installed but I am a Linux user and I only checked that Windows boots up correctly.

•  As the first thing, I proceeded to updating BIOS to the latest version for Latitude 7400 which, as of today, 31-08-2021, is 1.13.0.
• I installed this BIOS version via F12 -> BIOS Flash Update. The update apparently worked fine in the sense that there were no errors reported.
• Next, I inserted a USB drive with an EFI/GPT Ubuntu 18.04 image to install this system.
• When I press F12, I can see the disk drive among "UEFI BOOT" options.
• When I go to F2 -> General -> Boot Sequence, I can also see the drive recognised.
• Also in F2 -> Secure Boot -> Secure Boot Enable is checked.
• Still in F2 -> POST Behaviour - > Fastboot is thorough.
• And again in F2 -> System Configuration -> USB Configuration -> Enable USB Boot Support is checked.

As far as I can see, the firmware is updated and configured to boot from the USB drive.

However, when I do select the USB drive to boot from through F12, I am greeted with a popup with a title of "Critical Error Message" whose contents is "No bootable devices found".

The popup is displayed on a white background with "Dell. SupportAssist | Pre-Boot System Performance Check" at the top.

When the popup displays, I can only click a Shutdown button, there is nothing else displayed.

Let me also add that I have this thread from Spiceworks and I have tried the disabling of SMM mitigation workaround exactly as it is described over there, to no avail.

I hope that I provided all the details necessary and that someone from Dell can help me. Feel free to PM me for the service tag.

Thank you.