Bootable hardware diagnostics are important to me. I was surprised to find that most that I try won't boot on the first UEFI motherboard I've ever bought (Dark Hero).
First, I'm mystified that the populating the Boot Menu with devices is flakey. Usually if media isn't bootable it won't even display on the Boot Menu. But then sometimes they all suddenly do. And often an inserted boot media won't show up until I reboot into the Boot Menu. I'm using both USB on USB2, and ODD boot media.
I've learned that some will boot if I put the motherboard into CSM (Compatibility Support Module) "Legacy OPROM Only" mode.
At first I thought the Boot Menu wasn't even working, because media I was trying would just immediately instead display the UEFI BIOS Settings without any message.
That was in the default UEFI, before I enabled CSM and switched it to strictly "Legacy OPROM" mode. In the latter mode I at least get a message on boot fail:
"Reboot and Select proper Boot device or Insert Boot Media in selected Boot device and press a key"
Most recent BIOS 3401