Farm Workforce Modernization Act of 2021 This bill contains provisions related to alien farmworkers, including provisions establishing a certified agricultural worker (CAW) status and changing the H-2A temporary worker program. The Department of Homeland Security (DHS) may grant CAW status to an applying alien who (1) performed at least 1,035 hours of agricultural labor during the two-year period prior to March 3, 2021; (2) on that date was inadmissible, deportable, or under a grant of deferred enforced departure or temporary protected status; and (3) has been continuously present in the United States from that date until receiving CAW status. The bill imposes additional crime-related inadmissibility grounds on CAW applicants and makes some other grounds inapplicable. CAW status shall be valid for 5.5 years and may be extended. DHS may grant dependent status to the spouse or children of a principal alien. An alien with a pending application may not be detained or removed by DHS and shall be authorized for employment until DHS makes a final decision on the application. A CAW alien (and dependents) may apply for lawful permanent resident status after meeting various requirements, including performing a certain amount of agricultural labor for a number of years. DHS shall create an electronic platform for (1) filing H-2A petitions, (2) facilitating the processing of H-2A cases, and (3) providing agencies a single tool for obtaining H-2A-related case information. The bill makes various changes to the H-2A program, such as (1) modifying the method for calculating and making adjustments to the H-2A worker minimum wage, (2) specifying how an employer may satisfy requirements that it attempted to recruit U.S. workers, (3) requiring H-2A employers to guarantee certain minimum work hours, (4) making the program available for agricultural work that is not temporary or seasonal, and (5) reserving a visa allocation for the dairy industry. DHS shall establish a pilot program allowing certain H-2A workers to apply for portable status, which gives the worker 60 days after leaving a position to secure new employment with a registered H-2A employer. DHS shall establish an electronic system patterned on the E-Verify Program for employers to verify an individual's identity and employment authorization. Employers hiring individuals for agricultural employment must use the system. This bill permanently establishes the Housing Preservation and Revitalization Program, which provides financing assistance for rural rental housing and off-farm labor housing and rental assistance for qualified tenants of such housing. It also authorizes the Department of Agriculture to provide various assistance, including funding for insuring loans and grants for new farmworker housing.