1. Are these high bar or low bar? SS style is a low bar back squat.
2. Drive your hips UP, not back. See your knees going backwards as you come out of the hole? Drive hips UP.
3. What is your perception of a good squat? These is going to be some forward lean necessary to do these correctly - for some lifters more than others depending on factors such as bodily proportions, bar position and stance. I see what you're looking at on the last rep of video 1, but it's caused by the hips moving back instead of just up. Fix that. Your back will not be vertical on a low bar squat. This is not a front squat.
I'd like to see a back and a 45* camera view to see other things, but you don't have a forward lean issue right now. Think about it this way:
If your stance is good, you set the knees in the correct position, your hips are doing their job, and the bar is over the middle of the foot, then guess what? The back is probably in the right position. If you try to make it artifically more vertical, then you alter the mechanics of the movement.
The squat is a geometrical system that must be in balance. Alter the length or angle of one component and the others have to move, too.
I see hips moving back instead of up out of the bottom. That's the first thing that strikes me as needing a correction. I'd like to see your stance, too. And I want to know if your knees are staying out, which I can't see from this angle.
Have you ever tried oly shoes? I like squatting with a small heel.
I don't see anything so major that it would totally stunt progress (even though I stand by what I said about your hip drive) but at this BW and this bar weight it would be atypical for you to be stalled out with good recovery.
I see a slightly tilted bar (see it?) and a position that I *think* is high bar, but can't see enough on video. And that's fine if you want high bar. If not, review that chapter in SS.
Yep, I'm with BareSteel re: the knees. They are caving in on the way up--either make an effort to push them out harder or reduce the weight to allow your adductors to catch up in strength. The bar seems kind of high on your back, too.