New to the site and have done a few searches which talk about duck feet and how it’s a problem but don’t link to any videos or references for correction directly. For the folks that have corrected duck feet or splay foot I’d be curious as to what stretches/exercises you used.
Try addressing hip flexion and IR. Ideally we want around 120 degrees of hip flexion and 30-45 of hip internal rotation. Here is a video link on a duck foot correction MOB: