Fuel Choice and Deregulation Act of 2021 This bill revises requirements governing the use of alternative fuels in vehicles. Among other things, the bill revises requirements on aftermarket vehicle conversions that enable older vehicles to use alternative fuels. Under current law, the Environmental Protection Agency (EPA) must certify such conversions. This bill removes such certification requirements. The bill also bans the EPA from prohibiting or controlling biomass fuel. In addition, the bill revises the Corporate Average Fuel Economy standards for certain vehicles that are able to operate on something other than petroleum-based fuel, such as electric vehicles. Finally, the bill revises the Reid Vapor Pressure (RVP) requirements to provide for the year-round sale of ethanol-gasoline fuel blends that contain more than 10% denatured anhydrous ethanol. RVP is a metric of gasoline volatility (i.e., how quickly fuel evaporates into the atmosphere). Current law prohibits the sale of gasoline that exceed certain RVP limits during the high ozone season (i.e., the summer months). However, current law provides waivers from this requirement, including a waiver that gives certain ethanol-gasoline fuel blends containing 10% denatured anhydrous ethanol a higher RVP limit under certain conditions. This bill expands the waiver to include ethanol-gasoline fuel blends containing more than 10% of such ethanol, thus allowing year-round sales of such fuel blends.