Ankles are the usual culprit
If your heels lift or you fall forward, limited ankle dorsiflexion is likely stopping you. Do ankle mobility drills, stretch your calves, and try a small heel raise or lifting shoes to instantly gain range.
Most depth issues are ankle and hip mobility plus bracing; work those, widen your stance, and drive your knees out.
Poor depth is usually tight ankles, tight hips, or a stance that fights your hips, not weak legs. Improve ankle dorsiflexion with calf and ankle mobility, try slightly heeled shoes, and widen your stance with toes turned out. Actively push your knees out and keep your chest up as you sink. Practice to a box or with goblet squats to groove hitting parallel or below.
If your heels lift or you fall forward, limited ankle dorsiflexion is likely stopping you. Do ankle mobility drills, stretch your calves, and try a small heel raise or lifting shoes to instantly gain range.
A stance too narrow jams the hips. Widen it a little, point your toes out 15 to 30 degrees, and consciously push your knees out over your toes so your hips have room to drop between them.
Goblet squats let the counterweight pull you into a deeper, upright position, and box squats teach you to hit a consistent depth. Practice these to build the pattern before loading heavy.
Most depth issues are ankle and hip mobility plus bracing; work those, widen your stance, and drive your knees out.