CODE EXAMPLE FOR CSHARP

how to make 3d field of view in unity

Collider[] rangeChecks = Physics.OverlapSphere(transform.position, radius, targetMask);

if (rangeChecks.Length != 0)
{
     Transform target = rangeChecks[0].transform;
     Vector3 directionToTarget = (target.position - transform.position).normalized;

     //DrawDebugRays();
     bool withinXZPlane = Mathf.Abs(VectorUtils.AngleOffAroundAxis(directionToTarget, transform.forward, transform.up)) < angle / 2;
     bool withinYZPlane = Mathf.Abs(VectorUtils.AngleOffAroundAxis(directionToTarget, transform.forward, transform.right)) < angle / 2;
     print(Mathf.Abs(VectorUtils.AngleOffAroundAxis(directionToTarget, transform.forward, transform.right)) + " < " + (angle / 2));


     if (withinXZPlane && withinYZPlane)
     {
          float distanceToTarget = Vector3.Distance(transform.position, target.position);

          if (!Physics.Raycast(transform.position, directionToTarget, distanceToTarget, obstructionMask))
               canSeeTarget = true;
          else
               canSeeTarget = false;
      }

      else
           canSeeTarget = false;
}

else if (canSeeTarget)
      canSeeTarget = false;

//in another script
using UnityEngine;
public static class VectorUtils
{
     public static float AngleOffAroundAxis(Vector3 v, Vector3 forward, Vector3 axis)
     {
         Vector3 right = Vector3.Cross(axis, forward).normalized;
         forward = Vector3.Cross(right, axis).normalized;
         return Mathf.Atan2(Vector3.Dot(v, right), Vector3.Dot(v, forward)) * MathUtil.RAD_TO_DEG;
     }
}

Source: https://www.youtube.com/watch?v=j1-OyLo77ss
Source: https://forum.unity.com/threads/vector3-angle-on-relative-axis.381886/

//used parts from both sources for any variables that are not 
//declared locally, just declare them as global variables and 
//use SerializeField if you want. It may be beneficial to look at
//the sources to see where they were going with their code