@YRMM
Might be worth hunting down a smaller mSD card (like a 2GB one) and formatting it to FAT32 with
something like this. Then chuck the uncompressed contents at the root.
Alternatively, you could give this
one a shot.
I highly doubt that the cart itself has been bricked by your previous attempts to get it to work since we aren't flashing any firmware, not that this cart has the ability to afaik.
Should those still not work, you could remove the screw from the back and send us a pic of the PCB since there is a chance someone here might just recognise which obscure clone variant it is.