By soldering the ends of the LED, do you mean the 4 earth connections? I should probably have clarified that the 4 “earth” connections only lead to earth when the mosfets connected to the LED is open. Each connection leading to earth is for either, R, G, B or W so they can’t be soldered together.
Sorry, my original comment was poorly written. While they do lead to earth, there is a mosfet in between each that receives a unique PWM signal. See the edit for more details.