Low-Income First-Time Homebuyers Act of 2021 or the LIFT Homebuyers Act of 2021 This bill establishes a program to provide fixed-rate 20-year mortgages for first-time, first-generation homebuyers whose incomes do not exceed a certain amount. These mortgages must be offered by the Federal Housing Administration (FHA) or the Rural Housing Service (RHS). Pricing terms must be established (1) such that monthly mortgage payments under this program are similar to a 30-year FHA- or RHS-backed mortgage, or (2) as are determined to be necessary to develop liquidity for securities backed by covered mortgage loans and expand program participation by eligible homebuyers. Additionally, program funds must be transferred to the Department of the Treasury for the purchase of securities backed by such mortgages.