Currently, nested objects are not filterable nor vectorized a per our docs:

Currently, object and object[] datatype properties are not indexed and not vectorized.

Future plans include the ability to index nested properties, for example to allow for filtering on nested properties and vectorization options.

Our team is currently working on that feature, and you can keep track of it here:
https://github.com/weaviate/weaviate/issues/3694

Thanks!