Movable mask to show Player behind wall

Godot Version

4.3

Question

I’m trying to make a wall around the player transparent.
To achieve this, I’ve created a mask.

I tried using this tutorial as a starting point:
https://www.youtube.com/watch?v=X7t9zUw71O8&ab_channel=devtoria
Unfortunately, this didn’t lead to success.
I wish there were a reversed option in Light_Mode → Light Only, like → Shadow Only.

Even with various shaders, I couldn’t make progress, for example:
https://godotshaders.com/shader/sprite-cut-out-cut-in-mask/
It didn’t work like i wanted. I couldnt put the mask to the Player Position

At first, I thought this would be simple, but I’ve now been stuck on this problem for two days.
Is there a solution for this?