In addition to performing all the standard steps to share data, which privilege must be...

In addition to performing all the standard steps to share data, the USAGE privilege must be granted on each database referenced by a secure view in order to be shared. When sharing a database or specific objects like secure views, the receiving account needs to have the USAGE privilege on the database and schema to access the shared data. This privilege enables the receiving account to access the database and its schemas but does not allow for any DML operations. It's a prerequisite for accessing any objects within the database.

For a secure view to be part of a share, not only does the view itself need to be shared, but the underlying database (and schema, if applicable) must also be accessible to the recipients. Granting USAGE privilege on the database ensures that the receiving account can access the database in a read-only mode to utilize the shared view.

References:

Snowflake Documentation on Shares: Creating and Managing Shares