Augmenting Compatibility and Competition by Enabling Service Switching Act of 2021 or the ACCESS Act of 2021 This bill requires large online platforms (e.g., YouTube, Salesforce) to facilitate consumers and businesses switching from one platform to another. Specifically, the platforms must maintain interfaces that (1) securely transfer user data to other platforms (i.e., portability), and (2) allow other platforms to connect and communicate with their systems (i.e., interoperability). The bill provides the Federal Trade Commission (FTC) and the Department of Justice with the authority to designate specific platforms to which these requirements apply. After a platform is designated, the FTC must issue standards of interoperability specific to the platform. A platform may not change its interoperability interface without petitioning the FTC, and the platform must provide to competing businesses documentation for accessing the interface. Further, the FTC must establish a technical committee to assist with the implementation of these requirements. The bill provides the FTC with authority to enforce these requirements including through recovery of civil penalties and injunctive relief.