tl;dr on butt wink
To fix butt wink, follow these rules…
Make sure the knee, hip, and ankle can bend; if they don’t, limit squat depth
Squat with a neutral spine and whole foot pressure in the ground
Consider priming good technique by using a heel elevation or weight in front of the body like in the heels-elevated goblet squat
Lower training volume if fatigue negatively impacts technique
Keep training weight reasonably challenging so that exercise technique remains at minimum 90% perfect