How to display a "Game Over" after death?

you could do it in script just make a bool that checks when player is dead then display a GUI or a GUItext.

I can give you an example script for one option I have no experience with the game object GUItext. Here is a script I made for respawning my player when he dies. I will put a comment for what part you might be interested in this should work for what you want and if some stuff needs explaining I can help. public class PlayerRespawn : MonoBehaviour { //Public Variables

 public float ReSpawnTime = 0f;
 
 private int RespawnIndex= 0;
 private Camera MainCamera;
 public Transform[]ReSpawnLocation = new Transform[4];//Array For All My Repsawn Locations
 private PlayerVitals Pv;
 private GameGUI Gg;
 private bool ShowRespawnButton = false;
 public GameObject Player;
 //public Vector3 CameraPos = new Vector3(0,0,0);
 void Awake()
 {
 MainCamera = Camera.main; // Grab a reference to the camera
 
 //MainCamera = GameObject.FindWithTag("MainCamera");
 Gg = MainCamera.GetComponent();
 
 //Pv = GetComponent();
 Pv = GameObject.Find("Player").GetComponent();
 //Pv = Player.GetComponent();
 }
     // Use this for initialization
 
 void Update()
 {
 if(Pv.Life <= 0)
 {
 Dead(IsDead:true);
 
 //Debug.Log (ReSpawnLocation[RespawnIndex].name);
 
 }
 }
 **void OnGUI()
 {
 if(ShowRespawnButton)//This would be what you want
 if(GUI.Button(new Rect(10,10,75,40),"Respawn"))
 {**
 
 StartCoroutine("Respawn");
 }
 }
 
     //Method That ReSpawns The Player
    IEnumerator Respawn() 
 {
 yield return new WaitForSeconds(ReSpawnTime);    
 RespawnIndex = Random.Range(0,ReSpawnLocation.Length);
 Player.transform.position = ReSpawnLocation[RespawnIndex].position;
 MainCamera.transform.position = Player.transform.position;
 MainCamera.transform.localPosition = new Vector3(0f,0f,-15f);
 
 Pv.Life = Pv.MaxLife;
 Dead (false);
 yield return 0;
 StopCoroutine("Respawn");
 //Debug.Log ("Respawned");
 
 
 }    
 
 private void Dead (bool IsDead) 
 {
 
 
 if(IsDead ==true)
 {
 ShowRespawnButton = true;
 Gg.ShowGui = false;
 Player.renderer.enabled = false;
         
 //Debug.Log("you died");
 
 
 
 
 
 
 }
 
     
 if(IsDead==false)
 {
 ShowRespawnButton = false;
 Player.renderer.enabled = true;
 //StartCoroutine("MoveToTarget");
 //Debug.Log(IsDead);
 
 }
     }
             
 
 
 }