@new_to_me901 Okay, the spacers you used are high enough, the board does not rest on the metal as I feared. But you (and the other guy who made the plastic frame as well btw) ignored this part of the manual:
Do not use metal washers under the mounting screws, or screws with large heads (e.g. button head). Nylon washers are recommended and supplied with the board. With a metal washer or large screw head there is a risk of creating a short.
I do not know which parts the screws you used might have contacted, but you should definitely add the supplied washers between screw head and PCB.
A second issue may arise due to the hand-bent metal elements that are far from being even or even parallel to each other. If you tighten the screws on those, the PCB will get bent since each screw tries to force it to be parallel with the corresponding contact surface - which is something you should avoid if you want to keep it working for longer. Therefore yes, the alternative holder is definitely the better choice. Just use any non-conductive (!) plastic you have available for printing - standard PLA, PETG etc. will be fine. Just keep away from any plastic that is marketed as "conductive", "for shielding", "ESD" or such. If in doubt, check with a multimeter to be sure. With your Duet seemingly being in open space, you probably won't need active cooling (depends on your stepper current though).
However, the pictures do not clearly show a reason for the death of the Duet unless I overlooked something. Apart from updating the mounting frame, I therefore suggest you do check and clean up your wiring.