504 Modernization and Small Manufacturer Enhancement Act of 2021 This bill modifies the Small Business Administration (SBA) 504 Loan Program, which provides a small business with SBA financing—through a certified development company (CDC) intermediary—for expansion or modernization. Specifically, the bill adds policy goals, at least one of which a CDC must demonstrate to be eligible for assistance. These include (1) enhancing the ability of a small business to reduce costs by using energy efficient products and generating renewable energy, and (2) aiding the revitalization of any area for which a disaster has been declared or determined. The bill also authorizes a CDC to take specified actions to facilitate the closing of a 504 loan, such as correcting borrower or lender information on loan documents or reallocating up to 10% of the cost of a project. For small manufacturers, the bill (1) increases the maximum loan amount from $5.5 million to $6.5 million, (2) reduces the amount that they must contribute to project costs, (3) increases job retention requirements, and (4) revises collateral requirements and debt refinancing considerations. Further, each SBA district office must partner with a resource partner to provide certain training for small manufacturers.