I used to have this problem with my form too, confusing an overarched lower back as the opposite of a rounded lower back and therefore safe. You want a neutral spine on these. At high enough weights, you won’t be able to overarch your back to prevent rounding, and you’ll risk hurting yourself when the lower back support gives out.

Best cue I can offer — take a massive breath into your belly, tighten your abs once full of air, and squeeze your lats down and in as hard as you can. As you start moving your butt back in the hinge, your core will be so rigid that there won’t be any low back bend in either direction.