The board uses D2 (GPIO 4) as data line (or GPIO 21 when running on the ESP32). Since the same line is used as SDA for I2C modules it cannot be used in conjunction with I2C shields.
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Please note that D2 (GPIO 4) is also used as I2C SDA signal. For this reason the WS2812B cannot run together with an I2C shield.
From the software point of view a driver is already available in the micro Python library named neopixel. Accessing the WS2812B using this driver is the pretty simple.
Here is a program demonstrating this: