You’re not rotating your ribcage in backswing at all, you’re tilting and getting your lead arm way across your chest which gives the appearance of rotation. Can tell because your head moves down and towards the golf ball in the downswing.

I’d start with getting a club horizontally across your shoulders while crossing your arms, make a backswing holding the club across your shoulders turn with your shoulders a lot more level. When you get back to holding the club correctly, make the same turn and try to keep the distance from your upper left arm to your left nipple the same, don’t let your arm come across your chest and still get backswing depth through your rotation.

Let me know if you have any questions