Apologies. The dumb ISP-provided MUA sent on a <TAB> in the middle of a text line. !!??

Though mostly happy with Beowulf, compatibility with new stuff is crumbling, so I've bought a little Geekom A5 for switching horses to the latest Devuan, and:

Downloaded: devuan_excalibur_6.0.0_amd64_desktop.iso

$ sudo dd if=~/Downloads/devuan_excalibur_6.0.0_amd64_desktop.iso of=/dev/sda bs=512k

Plugged the iso into the left front USB socket on the A5, powered up & tapped <delete>, to invoke the BIOS.

In the "Boot" menu, have selected:

"New UEFI OS Boot Option Policy":   [Place First]

"Boot mode select:"              [LEGACY]

"FIXED BOOT ORDER Priorities":

Boot Option #1:     [USB Key]

The remaining boot options then auto-organised, with:

Boot Option #2:      [Hard Disk]

Boot Option #3:      [NVME]

etc., but relevant only after I manage to boot off the USB stick.

F4: Save & Exit

Despite some blinking of the USB stick's LED, there was no boot - instead a return to the BIOS.

In an effort to effect a legacy boot, I've tried in the "Security" ->"Secure Boot" menu to switch to:

"Secure Boot"          [Disabled]

thinking that might be needed to kill the UEFI gumpf. But I'm still stuck in the BIOS loop - no boot. It does display "Not Active" with either setting, so it doesn't look like the problem.
That menu does display at the top:

"System Mode"      User
but its parent "Security" menu states "In Setup the User will have Administrator rights." and the changes I make are remembered across BIOS reentries, and there's no objection to the changes I make.

There were no such issues when I installed Beowulf on an Intel NUC a few years back. I'll keep googling, but any hints from those who update a bit more often, and have some of this stuff tamed, would be most gratefully received.

(I really need to upgrade gcc-avr and kicad beyond what's on Beowulf, and a newer firefox would be a boon.)

Erik