i'm trying
float d = texture(DEPTH_TEXTURE, UV).r; ALBEDO.rgb = vec3(d, 0, 0);
and
float d = texture(DEPTH_TEXTURE, SCREEN_UV).r;
but everything is red. how to sample it in a right way?
It's because you are setting the albedo to only use the red channel.
If you do this it should work:
ALBEDO.rgb = vec3(d);
This will set all color channels to the same color giving you a grayscale image.
Note you will still have to transform the depth either to linear or adjust it to get a usable value.
https://docs.godotengine.org/en/3.1/tutorials/shading/screen-reading_shaders.html