If you are looking at the schematic, you’ll see the power supply on the right hand side of the diagram. Line and neutral come out of the power supply and go right up to the Main PCB. It’s a pretty short run.
Line goes from the power supply to the main PCB and then to the heater by a bit more circuitous route. It is not white or red. Take another look and see what you think.
5v and 12v are common DC voltages. Plus, if you look at the connectors, you’ll notice “ground”. That’s another hint that you’re looking at DC voltage, which requires its own ground.