Can't call Open3d inner functions?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### Steps to reproduce the issue

Friends, recently in the use of open3d library, found that their use and others are not quite the same place. Figure 2: Some custom functions in open3d cannot be called after reading the pcd file or Mesh file.
The library functions in the cpu seem to be unable to be called

### Error message

```shell
///
```

### Open3D, Python and System information

```markdown
Python 3.8
Open3D 0.18.0
Window 10 x64
```

### Additional information