I just noticed this post about the model 100: Model 100 make flash error - #2 by dcavalari which mentioned a problem where basically you have to hold the prog key as you plug in the keyboard. Then pressed “enter” on a different keyboard and the firmware flashing worked. May not be applicable to the atreus, but figured it would be an easy thing to test. This was dated October 2022. @algernon may be able to suggest more options (?)