I want to start running this game, but I'm not sure what UV speed means, and whats the difference between UV speed and UV 100%. I am curious and would love to learn

Chex Quest follows the same rules as Doom. UV-Speed means you complete all the maps as fast as you can without dying. there is no UV 100% however UV-Max means pretty much the same thing. UV-Max means that the player has to complete all the maps, kill all enemies, and find all of the secrets.