Well the good news is your box isn’t bricked per se, I’d imagine that is an upgrade image though hence it won’t go over 5%, you need the full image for this to work.
Your box not booting CoreELEC is nothing to do with the DTB, I would image u-boot is missing from the eMMC and that is why you are getting no video signal.
One option that should work but I have not tested is to burn the S912 image and then add u-boot to it from that upgrade image. If you have access to a linux PC then it’s easy.
sudo dd if=aml_sdc_burn.UBOOT of=/dev/sdX bs=1 count=442
sudo dd if=aml_sdc_burn.UBOOT of=/dev/sdX seek=1 skip=1 bs=512
You would have to replace /dev/sdX with the device-node for your SD card, this method does not work with USB.
This is the u-boot I have extracted from that image aml_sdc_burn.UBOOT (912.5 KB).