Linux gives you a huge choice of user interfaces, Xfce, Cinnamon, Gnome, and many others. Which one is the fastest?

GPU

Start with your computer. Does your computer have a GPU, a Graphical Processing Unit? Some user interfaces can use a GPU for speed then switch to slower CPU processing on computers without a GPU.

The GPU might be a built in chip or an add-on card. There is a huge difference between the slowest and fastest GPU. The Cinnamon GUI will be faster with most GPUs.