What I am trying to achieve: add object under camera. so that I can move around using FPS controller with said object in front of me.
Problem: When I drag object under camera or create a new object under camera, it doesn’t show up properly. only a flatten black part of the origin object.
how to solve this or get around it to achieve what I trying to do.
Sounds like you have a scale set to zero.
The proper way to set scales:
https://discussions.unity.com/t/851227/2
NEVER set scale (or any part of scale) to zero or negative.
NEVER use Vector2 because that makes the third term (Z) zero.
ALWAYS use Vector3, and make sure that the .z is either 1.0f, or else your non-zero scale.
Similarly never set scale to Vector3.zero, especially in a UI, because this will cause layout divide-by-zeros and damage all your hierarchy.