I found the solution.
ThomasBBB_1-1717853016134.png
To get this output, I had to control (or right) click the x axis to bring up options. Then choose Size by..., then Other, then the column I wanted to use.
I'm putting the solution here so that I will find it when I forget next time. Perhaps others will too.
Dropping the intended variable into the size element on the right, as I did above, does not work.