FWIW, I have a 2021 RDX, and have transported 8' pieces of lumber (2x4) with the back seats folded down. I protected the seats and center console with towels. The wood came almost to the dash, but I was able to get my hand on the shift buttons with no problem. I suspect that if you put the ladder in with the wide (bottom) part first, you might be able to get a 6' ladder into the car. Some measuring first will give you your answers.
I transported a fresh 6-foot Christmas tree in my 2020 RDX with the trunk end towards the front of the vehicle (swaddled in a mover's blanket to protect the interior) with no problem or obstruction to driving. So I would say a ladder would fit.
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