selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"css selector","selector":"[name="username"]"}

Kodunuz çalışıyor, muhtemelen chrome ile alakalı bir durum. Şurada çözüm için öneriler sunulmuş bakmanızda fayda var.
Firefox kullanıyorum, denedim sıkıntı yok:

from selenium import webdriver
import time

driver = webdriver.Firefox()
driver.get('https://www.instagram.com')
time.sleep(5)
username_box = driver.find_element_by_name("username")
password_box = driver.find_element_by_name("password")
blue_buton = driver.find_element_by_xpath('//*[@id="loginForm"]/div/div[3]/button/div')
username_box.send_keys("x")
password_box.send_keys("x")
blue_buton.click()

Arka planda çalışması için:

pip3 install xvfbwrapper
sudo apt-get install firefox xvfb
from selenium import webdriver
from xvfbwrapper import Xvfb
import time

display = Xvfb()
display.start()

driver = webdriver.Firefox()
driver.get('https://www.instagram.com')
time.sleep(5)
username_box = driver.find_element_by_name("username")
password_box = driver.find_element_by_name("password")
blue_buton = driver.find_element_by_xpath('//*[@id="loginForm"]/div/div[3]/button/div')
username_box.send_keys("x")
password_box.send_keys("x")
blue_buton.click()

display.stop()