QGIS expression: Extract attribute of nearest point

Question

I have two layer of points: 'Measure' (> 2000 points) and 'Control' (5 points).

For each control and measure point, I have a "depth" attribute. I would like to display on symbology of "depth" attribute with the closest point.

For now I can draw a line to the closest point:

Using this geometry expression inside 'Control' symbology:

make_line ( 
    $geometry, 
    overlay_nearest(
        'Measure', 
        $geometry, 
        limit:=2
    )[1]
)

Now I want to display the difference of depth on this line (Sorry it is in french):

But i don t know how to extract the attribute "depth" from the geometry point I have in expression:

In this screen, 'resultPoints_e74212d8_6062_4c65_bdda_cfebd8bd679f' is my 'Measure' layer.

The real question is: How to extract attribute from a geometry point ?

In reality, i need to replace the 0 in this formula with the depth attribute of the closest point:

'XY:'||round(length(transform(make_line ( $geometry, overlay_nearest('resultPoints_e74212d8_6062_4c65_bdda_cfebd8bd679f', $geometry, limit:=2)[1]),
'EPSG:4326',
'EPSG:2832')),2)||'m - Z:'||round(0-"depth")||'m'

Answer 1

(The credit of the answer go to @pigreco) (You can copy paste the answer and i will delete this one)

To get the attribute 'depth' of the nearest point of another layer in a qgis expression:

overlay_nearest('<my_layer_id>', "depth")[0]

Replace <my_layer_id> in the formula with your layer id to compare.

To avoid issues try to have same EPSG codes in your two layers.