CRT overlay now is a CanvasLayer, that can be put on the viewport over all.

scenes/UI/Start.tscn

@@ -1,7 +1,6 @@
-[gd_scene load_steps=3 format=3 uid="uid://o0c5ir7543g1"]
+[gd_scene load_steps=2 format=3 uid="uid://o0c5ir7543g1"]
 
 [ext_resource type="Script" path="res://scripts/End.gd" id="1_jfc42"]
-[ext_resource type="PackedScene" uid="uid://cnp8h65468543" path="res://scenes/overlays/crt_overlay.tscn" id="2_6myhp"]
 
 [node name="MainMenu" type="Control"]
 layout_mode = 3
@@ -85,8 +84,5 @@ focus_previous = NodePath("../Button04")
 text = "Quit
 "
 
-[node name="CRT_Overlay" parent="." instance=ExtResource("2_6myhp")]
-layout_mode = 1
-
 [connection signal="button_up" from="CenterContainer/VBoxContainer/Button01" to="." method="_on_play"]
 [connection signal="button_up" from="CenterContainer/VBoxContainer/Button05" to="." method="_on_quit"]