Federal Rotational Cyber Workforce Program Act of 2021 This bill establishes a rotational cyber workforce program under which certain federal employees may be detailed among rotational cyber workforce positions at other agencies. This bill authorizes an agency to determine whether a workforce position involving information technology, cybersecurity, or other cyber-related functions in that agency is eligible for the program. Additionally, the bill requires the Office of Personnel Management to issue a Federal Rotational Cyber Workforce Program operation plan providing policies, processes, and procedures for detailing employees among rotational cyber workforce positions at agencies. The Government Accountability Office must assess the operation and effectiveness of the rotational cyber workforce program by addressing the extent to which agencies have participated in the program and the experiences of employees serving in the program.