Drills to stop swaying in backswing

Put a ball under your right foot (assuming you're right handed). Put it on the outer half of the ball of your foot so the outer portion of the foot is slightly off the ground.

Teach your body what rotating feels like. Don’t just focus on bottom half drills.

That being said, I try to wind up on trail leg like a coil, then release it when I’m at the top. Can’t sway and coil at the same time.

May also look into mobility drills

When you address the ball just prior to swinging put tension in your right knee by trying to twist your right foot (if you’re right handed) to the right while keeping it planted.

If you can sway back while doing that you’ll be the first person I know who can.