Can you go up to the Montparnasse Tower Bar for free and have some drinks?
I saw a website that said they are having a craft beer festival.

no, why would anyone buy a ticket then, although the observation deck area is enclosed, not the rooftop bar.

but no

There is a champagne bar on the enclosed top level, after you have paid for the elevator. Also a cheap and tacky snack bar. (Then you can go up to the outdoor top level.)

Frankly, I do not know the rules for the Ciel de Paris rooftop restaurant, but I'm quite sure that anything you could order there would cost more than the ticket for the tourist elevator.

The website I found regarding their craft beer additions basically lists the prices to access the rooftop, insinuating to me that you much pay to access the bar, in addition to prices of some menu items.

https://www.sortiraparis.com/hotels-...ooftop/lang/en

If memory serves, the lifts to the roof were separate and yes, per your link, TravelNerd, one must pay. Precovid there were some more stairs to the very top.

I don't recall needing a ticket for the other lift to the bar on the lower floor.....anyone remember?