if you need to pass extra stuff to spawn

MultiplayerSpawnerExtender.gs

extends MultiplayerSpawner

# Example of packing multiple data points into the single allowed argument
func trigger_player_spawn(id: int, spawn_pos: Vector2, player_name: String):
	var spawn_data = {
		"id": id,
		"position": spawn_pos,
		"name": player_name
	}
	# Call spawn with the single dictionary argument
	self.spawn(spawn_data)

# Cleanup logic with null checks
func _on_player_disconnect(id: int):
	# Ensure the parent/container node exists before calling get_children()
	var player_container = get_node_or_null("/root/Main/Players")
	
	if player_container:
		for player in player_container.get_children():
			if player.name == str(id):
				player.queue_free()
				break
	else:
		printerr("Error: player_container is null in _on_player_disconnect")

# Implementation of the custom spawn processing
func _init():
	self.spawn_function = _custom_spawn_logic

func _custom_spawn_logic(data: Variant) -> Node:
	# Unpack the dictionary passed from trigger_player_spawn
	var player_scene = preload("res://player.tscn").instantiate()
	player_scene.name = str(data["id"])
	player_scene.position = data["position"]
	# Assign other data as needed
	return player_scene