So, we had a “vacuuming” incident in our 2022 Solitude. I was coming down the stairs with the vacuum, and my elbow went through the screen door, breaking a piece of plastic.

I’ve fixed plenty of screen doors over the years, but I had no idea what this part is called.
I was thinking it must be a “vertical spacer,” or something along those lines, but some research taught me it’s a “mullion,” a “a vertical element that forms a division between units of a window or screen“
Finally knowing what it was called, I had to contact the manufacturer, who referred me to Lippert (Contact customerservice@lci1.com). I sent them photos of the screen door, and the part number of the door (sticker inside the door frame), and provided the RV’s VIN.
It arrived a few days later but was clearly wrong.

The one I’m needing to replace is on the left, and the one they shipped me is on the right.
Back to Lippert again, they apologized and sent me the correct one (another 10 days without a screen door).
They only charged me $7 for the first one, and nothing for the second one, but still….
Replacing it was easy.
First step was to remove the screws holding the horizontal bars.

Next, you need to loosen (but not remove) the screen door lever screws from the outside.

Once those are all removed, the lower horizontal divider moves down easily enough to slide the new mullion into place.

Only real pain is that, for whatever reason, Lippert assumed I could juggle four different screwdrivers while on a step ladder (why couldn’t they use the same screws? They’ll all the same size).
Somehow I managed.