Did you only try to boot from USB or also from uSD card?
I have tried both. I format the SD card with SD Card Formatter then burn the image on to it using the latest version of Rufus. I put the card in the SD car slot and power it on. I have tried the toothpick method as well but my understanding is the Amlogic devices’ boot sequence is, first SD, second USB, and then internal flash.
I think the initial toothpick method is needed for all TV boxes to boot from uSD/USB.
But if you also tried it, I’m out of ideas. Maybe the bootloader is indeed locked.
Amlogic Burning Tool with an Android Image for your box specs.
Thanks guys - you have been helpful but I am not able to resolve it so going to leave it here. In the future I managed to work it out, I’ll share my learning here!