Your pecs might be popping, but popping pecs don’t look good when your shoulders are hunched over.
To pull your shoulders back and show off those well-built pecs, you’ll need to be working your back more. Not just with any exercises, though, but with more rows and other horizontal pulls.
When your humerus is internally rotated you want to be combating that with more exercises that strengthen in the opposite direction. So think less about pecs, lats, and internal shoulder rotators, and more about mid-traps and external shoulder rotators.
Chest-supported rows are a useful way to hit your mid-traps without fatiguing your lower back. Combining them with a mini-band is an underrated way to further load your shoulder external rotators at the same time. You’ll need these if you’re at a desk, driving, or on your phone all day.