Based on the first and third photos you provided, it looks like the cable housing is not properly seated in to the barrel adjuster at the back of the derailleur. This could be causing extra friction on the cable and/or not allowing the cable to move through the barrel adjuster (i.e. - pinching the cable between the ferrule and the barrel adjuster rim). I'm not saying that this is definitely the issue, but it should be checked and corrected if wrong.

Lubrication of the hinge points on the derailleur might help if it's binding up, but don't use WD40 as that is a solvent, not a lubricant. I use Boeshield T-9 mostly for these applications.

After correcting the cable routing and lubing the hinge points, you may have to go through a basic adjustment procedure to get everything working correctly.