ersignee_ For what it's worth I don't think this is a code issue, I think it's something in the camera settings, I can't write for sure it's a bug or not because I haven't played with it enough in Godot 4 as I've been experimenting with lots of other stuff I just don't think it should be ruled out. If you haven't messed with the camera in the code beyond making the camera follow the player it won't be anything that you've done specifically just a default setting of some kind when the smoothing is enabled, my money is it being some kind of setting.
I'm bringing this up because I've encountered pixelation in the lighting before and others have encountered some strangeness in normalmaps so just wait and see what others think, these problems do get fixed in the other versions though if it does turn out to be something but good job for spotting it.