Florence Duomo line without dome climb?

Susan, the long line is for the main body of the cathedral as it's free and doesn't require a ticket/reservation. The dome, on the other hand, requires an advance, timed-entry ticket ($), which controls the amount of people on the narrow stairs at any given point, and the entrance to those stairs is in a separate location from the main cathedral entrance. Does this help?

https://operaduomofirenze.skiperformance.com/en/store#/en/buy

Editing to add:
Never say never but to my knowledge there is no such thing as a skip-the-line ticket to the cathedral, or not without a paid tour, anyway. There is an English tour offered by duomo; as it doesn't appear to allow me to provide a direct link, find it under the "guided tours" dropdown in the link I provided above.

An added wrinkle in these times of covid, all indoor venues, free or not, require your green pass (CDC card) to be checked, possibly your temperature, and they may limit the number of people inside.

As an example, in Rome, the line for the Pantheon was wrapped half way around the Piazza, in several visits pre-covid, I had never seen a line, just wander in.

Right now the lines to get inside the cathedral are unbelievably long. There is no timed tickets for the church itself. You may be able to get in without a wait by booking a guided tour. I was just there and literally saw lines all the way down the side of the Duomo. I just skipped it and went into the many other churches that had no wait. A few are even still free. I recommend Santa Trinita, which includes the Sassetti Chapel with frescos of the life of Saint Francis by Ghirlandaio.

I recommend Santa Trinita, which includes the Sassetti Chapel

I'll second that one, Jane! Ghirlandaio's frescoes in that chapel are fascinating as he painted the contemporary subjects in the pictures as they really looked, warts and all. Particularly interesting is the clothing of the period and glimpses of 15th-century Florence in some of the backgrounds.

https://www.wga.hu/html_m/g/ghirland/domenico/5sassett/frescoes/index.html

We found the interior of the duomo to be less interesting than the exterior, and less interesting than many other churches we visited as well. Along with Santa Trinita, some alternates you might want to consider are Santa Croce, San Miniato al Monte (a must, IMHO), Santissima Annunziata (don't miss the frescoes in the Votive Cloister), Santa Maria Novella, and Cappella Brancacci, among others.

While the baptistry of the duomo complex is undergoing restoration, half of it plus the wonderful ceiling (!!!!) can be viewed so try to take a gander at that one too?

Thanks, all. I will look at adding Santa Trinita to the itinerary. Santa Croce and San Miniato (hopefully with a Vespers service) are already on the list!
Yes, I have also heard (incl. from RS) that the Duomo interior is rather underwhelming. We may play that part by ear. There will be so much to see and do even if we miss going inside.

Two years ago, I was in Italy with a friend who had never been before. We waited in line for 2 hours and never got near the entrance. We finally had to leave to catch a train. I booked a guided tour for our trip next month directly through their website.

Last time we were in Florence (pre-2019) there were long lines for both the dome tour AND the Duomo -- so we kept walking and visited the cathedral itself later that day when the line was about 20 people. If you haven't seen the Baptistry, it's well worth getting tickets -- and the line was minimal.