Make line from each polygon centroid to each adjacent polygon centroid in QGIS

Question

In QGIS I would need a Geometry Generator expression to, from a polygons layer, draws a line from the centroid of each polygon to the centroid of each adjacent polygon

Answer 1

Use this expression:

collect_geometries(
    array_foreach(
        overlay_intersects (@layer, centroid ($geometry)),
        make_line (centroid($geometry), @element)
    )
)