WS2812 HELP. Need name of Unkown component
It's most likely a decoupling capacitor meant to smooth out the voltage supply to the internal control chip.

This is standard practice to add to any chip. Power cables create a small bit of parasitic inductance in relation to the area between the lines. This inductance can induce voltage spikes when current draw changes significantly. A capacitor shrinks the effective area between the power lines.

This is also why the general advice for decoupling capacitors is to put them as close to the chip as physically possible.