'open3d.cpu.pybind.geometry.PointCloud' object has no attribute 'select_down_sample'

This error occurs when you are trying to call the method `select_down_sample` on a `open3d.cpu.pybind.geometry.PointCloud` object, but this method is not a valid attribute of this object.

The `select_down_sample` method is actually a method of the `open3d.geometry.voxel_down_sample` module, which can be used to downsample a point cloud by selecting only a subset of points at regular intervals.

To fix this error, you should import the `voxel_down_sample` method from the `open3d.geometry` module and use it to downsample your point cloud. Here is an example:

import open3d as o3d

# Load point cloud from file
pcd = o3d.io.read_point_cloud("input.pcd")

# Downsample the point cloud
downsampled_pcd = pcd.voxel_down_sample(voxel_size=0.05)

# Save the downsampled point cloud to file
o3d.io.write_point_cloud("output.pcd", downsampled_pcd)