Was there last week and...it was insane.
I tried to get a reserved-ticket and no dice, all sold-out. I went down in the AM and that was a mistake, half of the earth's population was there in front of the cathedral and the line was beyond anything a Disney-ride could conjure up. I considered coming back in the afternoon hoping things had calmed down but, I was already worn-out as I had already gotten in my 35k+ steps in that day.
As for checking IDs...it's good to have but, I've never been checked. Going to the Louvre, I could've had some fake/bogus QR code on my phone, flashed it to the security person and they just waved you through.