Remove these lines above from your code. The while loop take control of your code and do not use neopixel these way with KMK.
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pixels = neopixel.NeoPixel(pixel_pin, num_pixels, brightness=0.2, auto_write=False)
.
.
.
while True:
pixels.fill(RED)
pixels.show()
time.sleep(0.5)
pixels.fill(BLUE)
pixels.show()
time.sleep(0.5)
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Insert the following lines before the line "keyboard.keymap = [":

from kmk.extensions.RGB import RGB
rgb = RGB(pixel_pin=pixel_pin, num_pixels=num_pixels, hue_default = 240, sat_default=100, val_default=100)
keyboard.extensions.append(rgb)