Acess to the point cloud/mesh created by LiDAR with the new Ipad Pro

There currently isn't as simple way to do so (at least in ARKit 3.5). You can access the vertices and faces using ARMeshGeometry but that's raw data stored in a MTLBuffer. Let's hope ARKit 4.0 will provide more accessibility to raw data.

You can retrieve the generated mesh through ARMeshAnchor's geometry property, which is of type ARMeshGeometry and provides access to the vertices, faces, and normals. To see how to work with ARMeshGeometry, I recommend to check out the Visualizing and Interacting with a Reconstructed Scene developer sample.

If you're interested in how you can generate a point cloud, have a look at the
Visualizing a Point Cloud Using Scene Depth developer sample.

While ARKit doesn't have built-in export functionality, you have access to all required data to write your own code to export the mesh, for example to an OBJ file.

Is there an example for how the point cloud might be converted into geometry/mesh? I get that all the required data is there, but is there an example on how to convert that particle buffer into something that can be exported?

I think converting point cloud into a geometrical representation is a totally different topic. You would have to do something like Structure-from-Motion for 2D images or SLAM for LiDAR.