Thanks for your feedbacks and comments!
If the side to side means up&down, it is becauseThe camera limitation is a design choice that intends to prevent player walking while looking into the sky or the ground which will result them being even lost in the dark lol.
However if the side to side means left to right, then this will be a technical issue that if you dont play in full screen to hide ur cursor then the camera will be limited only to certain angle of movement.