@ nycboy
Online TurboTax is only for a 2019 return.
For a 2018 return, if you want to use TurboTax, you'll need to use 2018 desktop software (CD/download). But you won't be able to efile it; you'll have to file it by mail. I'll also tell you another option at the end of this post if you want to prepare it manually with forms and instructions from the IRS.
You can purchase 2018 desktop software as a download at this page and install it on your computer:
https://turbotax.intuit.com/personal-taxes/past-years-products/
Minimum system requirements for Windows version:
https://ttlc.intuit.com/questions/1901571-minimum-system-requirements-for-turbotax-windows-software
Minimum system requirements for Mac version:
https://ttlc.intuit.com/questions/1899173-minimum-system-requirements-for-turbotax-mac-software
The 2018 return cannot be efiled. It will need to be printed, signed, dated, and mailed. It's a good idea to mail by a method that has tracking, such as certified mail, priority mail, etc.
If you have both Federal and state returns, you need to mail each one separately to its respective tax agency.
If you are due a Federal refund, in normal times it would take about 6 weeks for the IRS to process a mailed return and deliver the refund. However, due to the Coronavirus, processing of paper returns is severely limited or shut down for the time being.
Or did you already start a 2018 return online prior to the 2018 online shutdown, and want to finish that one without starting over? If so, you can download the *.tax2018 data file from your account and finish it in the 2018 desktop software. If you already paid for your product previously, TurboTax Support should furnish you the software.
OR another option is to download the 2018 forms and instructions for free from the IRS website and fill them out manually.
https://www.irs.gov/forms-pubs/prior-year
