Hi, I am Dave, I will help you with this.
Clipchamp uses both the CPU and GPU for rendering/encoding videos.
It is not possible to change that however if you have a good dedicated graphics card, the best option would be to open the Settings App, then go to System - Display - Graphics and in there, add Clipchamp to the list and set it to run on your dedicated graphics card, that may increase encoding performance in Clipchamp.