Red light line appears on iphone 11

i believe it's a dot projector of camera. normally it's not noticeable, but at some circumstances, for example, in dark environment it becomes visible.

used for face detection together with infrared camera, refer https://www.thebestintech.com/what-is-dot-projector/#:~:text=The%20Dot%20projector%20in%20the,173%20dots%20on%20the%20face.&text=Every%20face%20comes%20with%20a,an%20exclusive%203D%20facial%20map. for details if interested

on my iPhone X it becomes visible rarely and only under special conditions, like darknes and/or with some view angle. in this case it's not a defect.

if it's always visible, i'd say it is and you should contact apple (or authorised) service for support and repair

if you see it every time then yes, it's very strange and not expected.

do you have any other problems? like slow face detection, battery drain etc?

well, then contact apple for repair/replacement