These parts are damaged or missing. It is a Pella window.
One pin is missing that fits into the slider that holds the window up.
The 2nd image is the pin on the other side. The 1st image is where the pin should be.
The 3rd image is the slot where the pin fits into. Notice that the slot is damaged. I can move one half of the slot and the other half does not move. The 4th image is a picture of the other side where the slot is not damaged. On the good side, the surfaces of the slot are parallel to each other.
I cannot see how to remove and replace the damaged slot and the plastic holder. It is too wide to come out of the vinyl window channel.