Flash drive does and does not boot with UEFI set in BIOS

Interesting problem so far. My Arch Linux flash drive will boot on one system with its BIOS set to UEFI but on the second system it will only boot with its BIOS set to Legacy only. Meanwhile, I want to prepare the second system with UEFI with encryption.

Meanwhile on the Arch Linux Installation guide - ArchWiki, it says, “…Arch Linux installation images do not support Secure Boot. You will need to disable Secure Boot to boot the installation medium. If desired, Secure Boot can be set up after completing the installation…”

I believe they mean secure boot in the bios settings. I couldn’t boot from the usb drive until I turned this off. It has nothing to do with disk encryption.

Yes, so I poking around more has not helped clarify this yet at all–no pond here; just an ocean. It’s my time to pause this pursuit and simply get on with a non-UEFI Arch installation already. I need to get an Arch install completed and dive deeper later.

Is the second system a laptop? If so you might have to select the UEFI file and set it to trusted in the BIOS.

If that’s not the case, is the partition table set to GPT?
When I tried to install a Linux distro to a dos partition in the past the installer failed because it was set to MBR/dos. Maybe this could be the problem.

Oops I read too fast, I thought you were having trouble getting UEFI installed on one computer. Is the drive listed in connected devices? Run “sudo fdisk -l” and look for your drive. If its there mount it with “sudo mount /dev/sdXX /mnt” Where XX is is the partition. For example it could be “/dev/sda1 /mnt” or “/dev/sdb1 /mnt”
After that go to the directory /mnt and your drives forders will be there.

You can also use “sudo df -l” to see all your partitions that are mounted and where they are mounted to, in case your partition is already mounted.

If it wasn’t listed, Is the drive formatted in NTFS? If it is maybe that could be the problem as that’s a windows partition. If it is formatted in NTFS and you have an extra hard drive laying around, transfer your files to that before formatting the drive into ext4 (or Luks if you want to encrypt it) because formatting erases everything. The Gnome Disks Utility is a great GUI program that I’ve used before to do this.