How to make a ''look behind feature'' FPS/TPS?

you can try it like this have a follow camera, and have another inactive camera that snaps to camera location, rotates, and rotates back when you release the input key, and deactivates

in my case, timeline is just a float track that goes from 0 to 165.

if you want to be able to look turning from both sides, make track from 0 to -165, and absolute one of the inputs

you might want to snap the camera location to 0,0,z first and lock x and y rotations while timeline is active, if not may not get what you want