Events, more

Enemy.gd

extends CharacterBody2D
class_name Enemy

@export var MoveSpeed : float

var player : Player

func _ready() -> void:
  Events.player_ready.connect(_on_player_ready)
 
 func _on_player_ready(player_node : Player) -> void:
   player = player_node
  
 func _physics_process(delta : float) -> void:
   if player != null:
     velocity = MoveSpeed * (player.global_position - global_position).normalized() # Simplest behavior: go straight at the player
    
   move_and_slide()

Events.gd

extends Node # Singleton script, no scene required, although you can use them for organization if you wish, just make sure you set the singleton to be the scene and not the script only

signal player_ready(player_node)

# That's all there is to this script so far! You can add more here if you have signals that apply to multiple possible other nodes and don't know when/if another node will ever even be added to the scene!

Player.gd

extends CharacterBody2D
class_name Player

func _ready() -> void:
  ... # Do all the readying you need, and make sure to include other things here
  
  Events.player_ready.emit(self) # And that's literally it. Because Events is a singleton, any game-object will necessarily be able to rely on it existing and so they know the signal exists. This is called delegating, or rather is one of the many definitions of delegating in programming. You're "delegating" the responsibility of holding the signal to some other node so that the nodes listening to/emitting that signal do not have to have the signal themselves.