As per the documentation here Searching | Joplin the Goto Anything feature on desktop allows searching tags by prefixing the search with # and searching for notebooks by prefixing the search with @
The search button on the initial screen on the mobile app does not support either of these queries, but it could be extended to be a Goto Anything search, by allowing these prefixes to be used.
While it is possible to filter tag names on the Tags screen (which is accessible when a note is opened), this is not particularly convenient, and wont allow you to view the notes associated with that tag unless you go back to the initial screen and enter a search using the tag: prefix. Regarding notebooks, it is currently not possible on the mobile app to filter notebook names.