shaders – Make part of albedo transparent

I have a shader which creates a circle inside of a plane mesh. I would like to get get rid of the parts around the circle, which are the r and b parts of the ALBEDO but I can’t seem to figure out how to do it.

The only thing I’ve managed to find is ALPHA but that changes the transparency of the entire shader and not just parts of it.

shader_type spatial;

float circle(vec2 position, float radius, float feather)
{
    return smoothstep(radius, radius + feather, length(position - vec2(0.5)));
}

void fragment() {
    ALBEDO = vec3(0, circle(UV - vec2(0), 0.5, 0.005), 0);
}

Which currently looks like:

enter image description here