all LEDs lit does not sound promising.. but.. I’ve been working on something. It’s not really ready for prime time but it might help here. Do you have Chrome or a chromium browser installed (Brave, etc.)?
So you’re holding the button down when you plug in the proxmark3? When you hold the button down, then while holding it down, you plug in the PM3, then you should get a white LED and two control LEDs should light up. If you have even a remotely modern bootloader on the board, after a couple seconds you can let go of the button and the LEDs should not change (it will stay in bootloader mode). Only very old legacy bootloaders require you to constantly hold the button down during the whole process.
