I’ve noticed this part on some video reviews about the ST, and others are missing it.
It’s listed as an “insulator” and covers the drivers side strut tower. I honestly can’t see any purpose to this other than maybe sound absorption.
Engine Compartment Insulator | FordUS
Insulator Part#: 3C078
Usages: LH Only, 05/06/2019, Explorer 2020-
My Nov 19 built ST is missing this part, along with rear air deflector.
View attachment 178197
View attachment 178198