High-bar back squat, upright torso, hit full depth.
Stay upright and let your knees travel forward, this is meant to be deep and quad-focused.
Racking the bar high on the traps keeps your torso near vertical, which sends the knees forward and the hips straight down, loading the quads through the deepest range a barbell squat allows. The glutes join hard out of the bottom, but this is the quad squat, the pattern weightlifters live in because it mirrors the catch position of the clean and snatch. Full depth is not a bonus here, it is the entire assignment.
Bar position and everything that follows from it. High bar keeps you upright, deep, and quad-dominant, low bar tips the torso over and shifts load to the hips and posterior chain, most lifters are a little stronger low bar but get more quad from high bar.
A raised heel helps a lot, it buys ankle range so you can stay upright at full depth. If you squat deep and upright regularly, lifting shoes are one of the few pieces of gear genuinely worth the money.
Deep knee bend is a position you train like any other, build the range gradually, control the descent, and load progressively. Lifters squat this way daily for entire careers, the depth is a skill, not a hazard.
