One further note, how are you powering the ESP?
If you’re using a separate 5V supply (or USB), remember to connect a ground line from the ESP to the LEDs so you have common ground for data (independent of power).
This is in addition to the proper levelshifter (don’t try and use I2C type), 74AHCTxxx based devices are best practice.
*don’t worry about the resistor. It is likely unneeded. If you are running 3 conductor wire with +,-,d in one and are running at longer distances and have white flickers now n there I would try adding a 33Ω resistor.
Is it absolutely necessary to connect all the channels? Is it absolutely necessary to connect the capacitor?
sorry for these questions, I want to make sure I’m doing the right thing.
100nF capacitor from pin14 to ground (place close to pin 14).
Tie pins 9,10,12,13 to ground or Vcc.
The capacitor prevents switching noise from adding flicker to the data.
If the extra pins are left “floating” they can cause also flicker in your LED data (you can ignore 8,11).
Connecting the ground lines together is not a problem (in fact it’s required).
Often the best way to do that for the data connection is to run a smaller data and ground wire together directly from the ESP to the strip, independent of the power wires that run to the power supply to the strip.