Social Media Disclosure And Transparency of Advertisements Act of 2021 or the Social Media DATA Act This bill requires consumer-facing websites and mobile applications with a large number of users to maintain advertisement libraries and make them available to academic researchers and the Federal Trade Commission (FTC). Each library must include, among other things, a digital copy of the advertisement content, a description of the target audience, and the number of views generated from the advertisement. The FTC and state attorneys general are authorized to enforce these requirements, and the FTC must use information from the advertisement libraries to enforce other laws within its jurisdiction. Additionally, the bill establishes a working group to address social media research access and make policy recommendations with respect to the information an interactive computer service (e.g., a social media company) should make available to academic researchers.