Louvre in the evening

It tends to be less crowded although much of the museum is not that crowded most of the time -- the really crowded areas are the handful of tourist must sees.

Note that some of the collections are closed evenings; we have more than once found the specific thing we came to see e.g. Egyptian Collection, Northern European Paintings, Coptic art, Rubens Room closed on the day we chose to see it in the evening. There is a list of what is closed that evening in the information desk area but you need to have a plan B if you were very focused on a particular thing.

What I like about the evening open times is that I visit more than once and break this fabulous, but really large site in to shorter visits. I concentrate one time on the 'big 3' and the galleries with the Italian and French paintings. Then I have another visit where I concentrate on the Greek/Roman/Etruscan statues and something I have never seen. It is so easy to become overwhelmed here.

I did a Friday late hours one August. Even in the room with the Mona Lisa, there were only 6 of us, so no problem spending time with her. Even if there was some congestion in the high tourist spots, I suspect waiting a few minutes means they will move off and you can have a few minutes of breathing space.
As noted, some sections are closed in the evenings.
For what it is worth, I got through the majority of it in my evening visit. Some areas I skimmed more than others. It also didn't help that it arrived that same day from North America, so a nap had helped, but jet lag reduced the memory retention of what I saw.

I was there just last month. Walked in around 8pm at the Pyramid entrance, only two other people ahead of me. The museum was still busy, but not as bad as I have seen it after 11 a.m. to early afternoon. Mona Lisa only had about 30 people in front of her. The disappointing part was the Marriage at Cana or Weddig at Cana painting was all covered up for refurbishment. It was very warm and stuffy in there at that time as well. Stayed until closing. They funneled everyone out through the lower level entrance/exit. The only exit opened was to the Metros, they locked the doors that head up to the gardin & Arch.