This information may be a little dated but it is directly from WD Staff and the indexing function may not have changed since the inception of the My Cloud Home since 2017.
It may be possible to avoid indexing by using the Public folder as MCH seem to treat that folder as a backup area and not common file storage. Alternatively, it is also quite easy and faster as well to mass copy files into a compressed (zip or 7z) folder such that those files are not detected to be indexed. Files within zip files can be viewed directly with something like Faststone Maxview.
