Pixhawk 2.4.8 vs 2.4.6

what is the main difference between the pixhawk 2.4.6 and 2.4.8

I’s mostly the same, please choose “Pixhawk 1” firmware when selecting the board type.

2.4.6 was an official reference board from 3DR and produced by some others (Mro). 2.4.8 is a bastard board with some hardware removed. But as @amilcarlucas says Pixhawk1 if the correct firmware.