Maybe the sound card really did burn out, at least it doesn’t seem to be recognised any more. Try disconnecting the sound card from the Pi and reconnecting it. Select „none“ as the sound card in the HiFiBerry plugin, restart the device, then select the HiFiBerry Digi again and restart again. If it is still not recognised, it is probably defective. Of course, you can also exchange the sound cards of your two devices to see which component is defective.