Simply because you moved a dtb into the root folder - doesn’t mean Coreelec ever used it. I feel certain that the bit of digging I have done on this box places it before the advent of dtb’s. People are using TWRP on these boxes which points to the old method.
Your pathway to a working box is
-find your original Android ROM
-reburn your android rom using AMLogic burn tool
-find a copy of TWRP which is designed for your specific box and burn it using what whatever instructions it comes with
-find a version of Libreelec packaged for your box and use TWRP to burn it to your box
A good place to start would be plouging through this Freaktabs thread:
Or try this thread which specifically outlines the procedure I described:
Be warned, when I found myself in a similar situation to this with my S812 box it took me weeks of hard work to get it back up and running. However I now still have this running a Krypton build so it was worth the weeks of effort it took (maybe).
Don’t come back asking questions till you have consumed this information in enough detail to try it yourself.