The TurboTax 2018 desktop edition is only available in Deluxe, Premier or Home & Business. You could not have purchased the 2018 Basic desktop edition in 2020 - https://turbotax.intuit.com/personal-taxes/past-years-products/
The TurboTax online editions are only for tax year 2019 - https://turbotax.intuit.com/personal-taxes/online/
What exactly have you purchased? What tax year are you trying to complete?
