Scene Switching in Godot 4

level_1.gd

# How to switch to a PackedScene
extends Node2D

@export var level_2_scene:PackedScene

func _on_level_2_button_pressed() -> void:
  get_tree().change_scene_to_packed(level_2_scene)

level_2.gd

# How to switch to a File resource path
extends Node2D

func _on_level_1_button_pressed() -> void:
  get_tree().change_scene_to_file("res://level_1.tscn")

scene_switcher.gd

# PREFERRED APPROACH
# Set up the Autoload singleton as a global variable and then use this like:
# SceneSwitcher.switch_scene("res://level_1.tscn")
extends Node

var current_scene = null
func _ready() -> void:
	var root = get_tree().root
	current_scene = root.get_child(root.get_child_count() - 1)

func switch_scene(res_path):
	call_deferred("_deferred_switch_scene", res_path)
	
func _deferred_switch_scene(res_path):
	current_scene.free()
	var s = load(res_path)
	current_scene = s.instantiate()
	get_tree().root.add_child(current_scene)
	get_tree().current_scene = current_scene