finding this particular data in a website using selenium or python

You can try to wait few seconds for required element to appear:

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

driver = webdriver.Chrome()
driver.get("https://www.zmrzlina-misa.cz")

time_to_wait = 5

try:
    element = WebDriverWait(driver, time_to_wait).until(
        EC.presence_of_element_located((By.XPATH, "//*[@data-optanongroupid]"))
    )
    print('Element with "data-optanongroupid" attribute found')
except:
    print('No elements with "data-optanongroupid" attribute found')

If it found add your code to try block, if not found – to except block