Consider using Callable.call_deferred() instead of Object.call_deferred()

This way you get to avoid a string reference

Say you have a signal: died, and inside on_died, godot gives you an error/warning and suggests you to on the add_child() line and suggests to use call_deferred

func _on_died():
	if randf() > drop_chance: return
	
	var vial_instance = vial_scene.instantiate() as Node2D
	owner.get_parent().add_child(vial_instance) #need to call_deferred

	vial_instance.global_position = owner.global_position

Instead of directly calling the add_child() method deferred,

Navigate to where the the signal is being emitted and use the Callable.call_deferred()

• Extract method

• Construct Callable

  <aside> ⚠️ Make sure you do not call the extracted method, simply pass the reference

  </aside>

• call call_deferred() on the Callable

func take_damage(damage: float):
	current_health = max(current_health - damage, 0)
	Callable(check_death).call_deferred()

func check_death():
	if current_health == 0:
			died.emit()
			owner.queue_free()

This way, you tackle the root of the problem and any other instances where you connect to the died signal wont have to call_deferred() individually every single time .

YOU DONT ACTUALLY NEED TO WRAP IN CALLABLE

You can actually just call call_deferred() directly on a method without having to construct a callable.

check_death.call_deferred()

You can take this a step further to avoid creating a seperate function by using a lambda

(func():
    if _current_health == 0:
        owner.queue_free()
        died.emit()
).call_deferred()

From: https://www.udemy.com/course/create-a-complete-2d-arena-survival-roguelike-game-in-godot-4/