Report Redshift Serverless Cost by Namespace

You can use the tags you set for AWS resources to analyze costs.
Available by activating cost allocation tags.
It may also take up to 3 days after activating the cost allocation tag for it to appear in Cost Explorer.
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/activating-tags.html

Filtering by tag can be done by following the steps in the following document.
https://repost.aws/knowledge-center/cost-explorer-analyze-spending-and-usage

View costs by cost allocation tag

To view costs by cost allocation tag, choose Tag for Group by. The Tag option isn't available if you have no cost allocation tags. When you create a new cost allocation tag, you might need to wait up to three days for the tag to appear in Cost Explorer.