Good view of the Eiffel Tower at night from Le Rive Droite?

I'd go to Trocadaro and look SE.

You may as well take the métro from Bercy all the way to the Trocadéro stop and take the steps up to the Palais de Chaillot to have the great view directly across the Seine from the Tour Eiffel. This is the perfect view, especially in the evening when the tower is lit up. You won't regret the time it takes to get there, and you'll probably want to linger there, if the view doesn't just pull you over the bridge to the tower itself. 'Magical' is the word.

https://www.ratp.fr/en

This official transit planner says the Bercy Metro station is five minutes walk from the arena. It estimates the ride to Trocadero at about a half hour. The station is behind the Troc plaza which offers unrivalled views of the tower. Line is M6.

From Bercy take the 14 ( direction St Lazare ) to Madeleine ( very few stops ) and switch to the 8 ( direction Balard ) , exit at Ecole Militaire . From there a short walk along Place Joffre puts you at the head of the Champ de Mars , The tower will be in front of you , plainly visible from top to bottom . Be there at the top of the hour for the twinkling light show .

Here are some snapshots of the Eiffel Tower from Trocadero -- at the end of this post

https://janettravels.wordpress.com/2016/05/16/the-eiffel-tower-in-the-rain/

This is fantastic, thank you everybody! Trocadero it will be. With sunset around 5:25, I can't wait to see the dazzling lights at 6pm! Your website looks fantastic Janet. We'll go if it rains!!

To return to our hotel located near the RER Luxembourg stop, it looks like we'll take the 6 to Denfert Rochereau and then take the RER B to Luxembourg. Is there signage at Denfert Rochereau for the RER B so we can easily make that transfer?

Paris metro, train and RER stations are all very well signed, just followed the RER B signs. I don't know how long a walk that transfer is, but even in the nightmare of Chatelet metro station with its 20+ exits and endless corridors, it is easy to find connecting trains or exits by following the signs.

Another vote for the Trocadero. Beautiful views at night and during the day.
Plus a great view of not only Eiffel Tower but almost all of Paris is from the top of the Montparnasse Tower (it was the tallest skyscraper in France until 2011, when it was surpassed by the 231-metre (758 ft) Tour First.) - you can take the metro there - get off at Montparnasse – Bienvenüe Station.

Ditto the recommendations on the Trocadero. Since you'll be in town overnight, why not take an evening cruise on the Seine? You'll get excellent views of the Tower that way as well, and the cruises are really relaxing and scenic.

I would say the best options are:

1.) River boat cruise on the Seine (way I first saw it and most memorable experience for me, not good for pictures)
2.) Trocadero (best for pictures but gets really crowded, very close to the tower)
3.) Montparnasse Tower Roofdeck (very overlooked, great views up here)
4.) View from one of the many bridges that cross the Siene like the Pont Alexandre III or any closer bridge crossings (good but you will likely want to be closer)
5.) View from top of Arc De Triomphe (requires a climb)

I have a few of these location examples on my page below:
https://www.mattreynoldsphotography.com/#/france/

Don't forget to not just wait for the tower to light up, but wait until the next hour on the hour for the 5 minutes when it will sparkle!!!
In my pictures there are a couple that show it sparkling compared to one where it is merely lit up.

View from one of the many bridges that cross the Siene like the Pont
Alexandre III or any closer bridge crossings (good but you will likely
want to be closer)

The Pont Alexandre III looks to be a shorter trip from Bercy than the Trocadero on a Saturday around 5pm according to Google Maps. Is it worth going the extra distance to the Trocadero? I'm guessing it is but I want to double check.

I've looked at the Trocadero pictures from Google images and it looks like there are benches. With my back, I would need some place to sit. Would this be a problem? I'll be there a week from Saturday so I'm not sure how crowded it would be.

Paris metro, train and RER stations are all very well signed, just
followed the RER B signs. I don't know how long a walk that transfer
is, but even in the nightmare of Chatelet metro station with its 20+
exits and endless corridors, it is easy to find connecting trains or
exits by following the signs.

What a relief. Thank you! Earlier next week, I'll also be taking the RER B and a bus to the Basilica of St Denis from Luxembourg RER station so I'm glad the signage is good. I don't know which route yet.

My favorite place to photograph the Eiffel Tower has been from under the middle arch of the Pont du Bir Hakeim. If you open the link below and scroll down, it's the fifth photo. It's about a 15 min. walk from the Trocadero. But I was there during daylight, not at night. The Place du Trocadero is a great choice, and if you have time and want to wander, have your GPS take you to the Pont du Bir Hakeim!

https://www.cntraveler.com/galleries/2014-11-10/where-to-get-the-best-views-of-the-eiffel-tower

The Pont Alexandre III looks to be a shorter trip from Bercy than the Trocadero on a Saturday around 5pm according to Google Maps. Is it worth going the extra distance to the Trocadero? I'm guessing it is but I want to double check.

Yes, it's worth going further to Trocadero as the view is MUCH closer.

Silly question, at the Trocadero, are there hotels nearby in case I need to use the bathroom/toilet? Or public toilets? I'm good with both. With my mother at a gas station outside of Ankara 18 years ago, I was happy to see a trough dug behind the station as I needed to do what I had to do. So I don't require posh surroundings. LOL

Vickie, thanks for the link! I might go to the Pont de Bir-Hakeim on my own earlier this week. What a perfect spot especially in the rain!

St. Denis is reached by metro 13 the Basilica St. Denis stop. The metro is just through a small market and around the corner to the Basilica which is located in the town square by the Hotel DeVille for St. Denis. No bus is required; it is a very easy trip.

St. Denis is reached by metro 13 the Basilica St. Denis stop. The
metro is just through a small market and around the corner to the
Basilica which is located in the town square by the Hotel DeVille for
St. Denis. No bus is required; it is a very easy trip.

Thank you!