Please use code tags with your posts so it's easier to read, makes a huge difference for people when debugging problems, also, I haven't been tinkering all that much with Godot 4 in 2D admittedly but I think you're using global_position wrong. This is just my personal preference as well but I'm not a fan of that style of coding where you dump a ton of variables in a function when you can access them just as well from the top.
To me you should be doing something like?
var effectPosition = global_position
Then call effectPosition that way, no need for explicit declarations in GDScript unless you've got a specific reason for it, looking at it a bit more I think you've done something odd possible with your PackedScene stuff too.
Edit: This is how I did pre-loaded scenes in Godot 4.
var plasmaBulletHole = preload ("res://plasma_bullet_hole_node.tscn")
Edit 2: Now that caffeine has kicked in I think you've mainly just declared the global position wrong which is why you're getting the error, the engine seems to think you're declaring it as a custom variable.
