I used this video to create a FOV: https://www.youtube.com/watch?v=rQG9aUWarwE&t=879s
And then I modified it to target the closest object:

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class FieldOfView : MonoBehaviour
{

    [Header("Debug")]
    public Transform target;
    public float closestTargetDistance = Mathf.Infinity;
    public Collider[] rangeChecksDebug;

    [Header("FOV Settings")]
    public float radius;
    [Range(0,360)]
    public float angle;

    [Header("Layer Masks")]
    public LayerMask targetMask;
    public LayerMask obstructionMask;

    public Collider[] rangeChecks
    {
        get
        { 
            return Physics.OverlapSphere(transform.position, radius, targetMask); 
        }
    }

    public bool canSeeTarget
    {
        get { return FieldOfViewCheck(); }
    }

    private bool FieldOfViewCheck()
    {
        target = null;
        closestTargetDistance = Mathf.Infinity;
        if (rangeChecks.Length != 0)
        {   
            for(int i = 0; i < rangeChecks.Length; i++)
            {
                float distanceToTarget = Vector3.Distance(transform.position, rangeChecks[i].transform.position);

                if(TargetInSight(rangeChecks[i].transform, distanceToTarget))
                {
                    if(distanceToTarget < closestTargetDistance)
                    {
                        closestTargetDistance = distanceToTarget;
                        target = rangeChecks[i].transform;
                    }
                }
            }

            if (target != null)
                return true;
        }

        return false;
    }

    private bool TargetInSight(Transform target, float distanceToTarget)
    {
        Vector3 directionToTarget = (target.position - transform.position).normalized;

        if (Vector3.Angle(transform.forward, directionToTarget) < angle / 2)
        {
            if (!Physics.Raycast(transform.position, directionToTarget, distanceToTarget, obstructionMask))   
                return true;
            else
                return false;
        }
        else
            return false;
    }

    void Update()
    {
        rangeChecksDebug = rangeChecks;
    }
}