There are many differences. Here are some highlights:
The Pixhawk 2.4.8 is a branch of the original open source 3DR Pixhawk 1. it is based on the PX4 FMUv2 standard:
The Pixhawk 4 is based on the PX4 FMUv5 standard:
The Pixhawk 4 features a more powerful M7 processor, whereas the Pixhawk 2.4.8 features the lesser M4.
Pixhawk 4 also has the JST-GH connectors which are far superior to the older DF13 connectors on the 2.4.8 ( and in reality these cheap chinese clones like what you have listed dont even use authentic DF13 - they use cheap “pico blade” knock offs)
Also, there is no GPS in the Pixhawk 2.4.8 you linked. You would have to purchase that separately. The Pixhawk 4 you linked comes with the GPS.
Be warned about those white colored Pixhawk 2.4.8 - many users have had issues with them.