update: I was able to do it using this code
coords_2D = Metashape.Vector([x, y])
sensor = camera.sensor
pc_pred = custom_chunk.point_cloud.pickPoint(camera.center, camera.transform.mulp(sensor.calibration.unproject(coords_2D)))
pc_pred.size = 4
pc_pred[3] = 1.
v=custom_chunk.crs.project((custom_chunk.transform.matrix*pc_pred)[0:3])