I have received and mounted my DevTerm A06 a few days ago.
I don’t know if my assembly is correct, as when I start the device (both with batteries or with a USB-C cable), the LED becomes green, but the fan is never spinning and the display never shows something.
Tons of things could have gone wrong. But green leds are good - power is getting to the carrier board. The fan won’t spin at boot, and even when it does you can barely hear it.
Try the easiest thing first:
Flash a different SD card and try again. Booting is slow and the screen seems dead for a while, then boot text should appear. It can feel like several minutes.
Next easiest thing to try is re-seat the display connector.