Hello mwhalen_635,
Welcome to Apple Support Communities. We understand that you're seeing a green line when using the front-facing camera on your iPhone 7+ while using FaceTime or Snapchat. We'd be happy to investigate this issue further with you.
Are you experiencing this behavior when using the built-in camera app on your iPhone? Does this occur with the rear- facing camera as well? Also, does the person you're chatting with see this green line or not?
To get started, let's try to restart your iPhone:
Restart your iPhone
iOS 14.0.1 was released recently, and may help with the issue you're experiencing, so if you haven’t updated to that, let’s do so now.
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
"Clean the front and back camera lenses with a microfiber cloth.If you see dirt or debris inside the lens or if the camera lens appears to be misaligned or blocked, contact Apple Support for help with your iPhone, iPad, or iPod touch."
If the camera or flash on your iPhone, iPad, or iPod touch isn't working
Let us know if that helps. We'll be looking forward to your response.