There's two ways your form can be "off": 1)you can be using safe, but suboptimal form; or 2) you can be using unsafe form.
These lists are not in any way comprehensive:
Thing's like not going low enough, excessive forward lean, some knee drift toward middle/not pressing your knees out, butt wink, feet not optimally placed or rotated, etc are not going to get you hurt, they will just limit how much weight you can do and/or strength/hypertrophy gains. Most people start doing some of these things as they start getting toward max weights. Very few, if any, people are doing "flawless" form squats on max or near max attempts.
For what it's worth, my recollection is that you just recently started doing SL5x5, so you shouldn't really be at a point where you are attempting max weights.
On the other hand, things like having the bar placed asymmetrically on your back, leaning to one side or the other, torquing to one side or the other, losing arch/tightness or rounding in your upper or lower back, putting the bar on your cervical spine, serious degrees of knee cave-in, etc are going to not only limit the weight you can do, but also put you at risk for injury.