To allow secure views the ability to reference data in multiple databases, the REFERENCE_USAGE privilege must be granted on each database that contains objects referenced by the secure view2. This privilege is necessary before granting the SELECT privilege on a secure view to a share.

Data classification in Snowflake is a feature that allows organizations to identify and categorize data stored in tables or columns based on its sensitivity level or content type. This feature can be used to find sensitive data within the database by classifying data as confidential, personal, public, etc., making it easier to apply appropriate security measures, such as masking policies or row-level security, to protect sensitive information.
References:
* Snowflake Documentation: Data Classification

In Snowflake, to create a materialized view, the user must have the necessary privileges on the schema where the view will be created. These privileges are granted through roles, not directly to individual users. Therefore, the correct process is to grant the role to the user and then grant the privilege to create the materialized view to the role itself.
The statement GRANT ROLE MYROLE TO USER USER1; grants the specified role to the user, allowing them to assume that role and exercise its privileges. The subsequent statement CREATE MATERIALIZED VIEW ON SCHEMA MYDB.MYSCHEMA TO MYROLE; grants the privilege to create a materialized view within the specified schema to the role MYROLE. Any user who has been granted MYROLE can then create materialized views in MYDB.MYSCHEMA.
Reference:
Snowflake Documentation on Roles
Snowflake Documentation on Materialized Views