Chase the Player

An enemy that chases the player needs a Rigidbody, so walls stop it and it can push and be pushed. The chase itself is a velocity aimed at the player, set once per physics step. This zombie walks toward whatever is in its player slot:

[SerializeField] private Transform player;
[SerializeField] private float speed = 2.5f;
private Rigidbody rb;

void Start()
{
    rb = GetComponent<Rigidbody>();
}

void FixedUpdate()
{
    Vector3 toPlayer = player.position - rb.position;
    toPlayer.y = 0f;
    Vector3 dir = toPlayer.normalized;
    rb.linearVelocity = new Vector3(dir.x * speed, rb.linearVelocity.y, dir.z * speed);
}

player.position - rb.position points from the zombie to the player. Its y is set to 0 so the zombie walks level when the player stands higher or lower, and normalized gives it length 1, so the zombie walks at speed whether the player is 2 units away or 20. The new velocity keeps the old y velocity, so gravity still pulls the zombie down off a step. Its Rigidbody has Freeze Rotation on, so it does not tip over as it walks.

A velocity you set makes a walker that starts and turns at once. A heavy enemy, such as a rolling barrel, is pushed with AddForce in the same FixedUpdate instead: it gathers speed, keeps its momentum and overshoots when the player steps aside.

Vector3 toPlayer = player.position - rb.position;
toPlayer.y = 0f;
rb.AddForce(toPlayer.normalized * push);

Avoid moving a chaser's Transform: that places it inside a wall as readily as anywhere else, and the physics engine can only push it back out afterwards.