TT Online is only good for 2020. You would have to purchase and download the desktop software for each of the prior years, and file by mail. TT currently supports 2017, 2018 and 2019.
TurboTax® 2017 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)
TurboTax® 2018 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)
TurboTax® 2019 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)
Federal refunds for earlier years are time-barred, but some states have longer Statutes of Limitations.
