webscrapping with returning empty list

Yo need to wait until page will completely loaded:

driver.get(url)
timeout = 5
try:
    element_present = EC.presence_of_element_located((By.CLASS_NAME, 'content-review'))
    WebDriverWait(driver, timeout).until(element_present)
except TimeoutException:
    print("Timed out waiting for page to load")
soup = BeautifulSoup(driver.page_source, 'lxml')
for review in soup.find_all('div', class_='content-review'):
    print(review.getText().strip())

Add necessary libs:

from selenium import webdriver
from selenium.common.exceptions import TimeoutException
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By

OUTPUT:

Super Shampoo, meine Haare glänzt und sind sehr weich. 
Ich verwende dieses Produkt seit kurzem und ich bin begeistert, so ein pflegendes Shampoo habe ich noch nie gehabt. Er gibt meinen Haar Glanz, Geschmeidigkeit und Fülle. Ich kann es nur empfehlen.
Zufrieden
Tolles Shampoo
Sehr gut

Second option - find request with reviews and get data:

url = "https://staticw2.yotpo.com/batch/1eunvtBQrA7MbZslPu3gAznkZCUjvEeL5tp0uybR/80053469-250"

payload='methods=%5B%7B%22method%22%3A%22main_widget%22%2C%22params%22%3A%7B%22pid%22%3A%2280053469-250%22%2C%22page%22%3A2%2C%22order_metadata_fields%22%3A%7B%7D%2C%22widget_product_id%22%3A%2280053469-250%22%7D%7D%5D&app_key=1eunvtBQrA7MbZslPu3gAznkZCUjvEeL5tp0uybR'
response = requests.request("POST", url, data=payload)
soup = BeautifulSoup(response.json()[0]['result'], 'lxml')
for review in soup.find_all('div', class_='content-review'):
    print(review.getText().strip())

With same output

Main issue here is that you need to close 'accept cookies' popup which is located in shadow DOM.

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.common.exceptions import NoSuchElementException
from selenium.common.exceptions import ElementNotInteractableException
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
import time

driver = webdriver.Chrome()
# OR: driver = webdriver.Chrome(executable_path='D:\Downloads\chromedriver\chromedriver.exe')
url = 'https://www.flaconi.de/haare/kerastase/chronologiste/kerastase-chronologiste-bain-regenerant-haarshampoo.html?yoReviewsPage=2'
driver.get(url)

webdriverWaiter = WebDriverWait(driver, 20)

webdriverWaiter.until(EC.text_to_be_present_in_element_attribute((By.CSS_SELECTOR, "body"), "class" ,"overflowHidden"))
shadow_host = driver.find_element(By.CSS_SELECTOR, '#usercentrics-root')
shadow_root = shadow_host.shadow_root

accept_cookies_button_css = "button[data-testid='uc-accept-all-button']"

# wait for accept cookies button to appear
accept_cookies_button = None
while not accept_cookies_button:
    try:
        accept_cookies_button = shadow_root.find_element(By.CSS_SELECTOR, accept_cookies_button_css)
    except NoSuchElementException:
        time.sleep(1)

# click accept cookies button
clicked = False
while not clicked:
    try:
        accept_cookies_button.click()
        clicked = True
    except ElementNotInteractableException:
        time.sleep(1)

content_review_css = ".content-review"
webdriverWaiter.until(EC.visibility_of_element_located((By.CSS_SELECTOR, content_review_css)))
reviews = driver.find_elements(By.CSS_SELECTOR, content_review_css)
for rev in reviews:
    print(rev.text)

Popup image: