@timsynonym asked: "Can I file 2019 and 2020 together?"
That's a big NO!! You cannot combine two tax years in one return. Income from each tax year must be reported separately in the specific return for the corresponding tax year. Online TurboTax is currently only for a 2020 return.
2019 income must be reported in a 2019 return. If you want to use TurboTax to prepare a 2019 return, you'll need to use 2019 desktop software (CD/download). You can purchase 2019 desktop software directly from TurboTax as a download at this page and install it on your computer:
https://turbotax.intuit.com/personal-taxes/past-years-products/
You may be able to find the 2019 software cheaper at a reputable authorized retailer like Amazon, but even there be sure it is a legitimate authorized product from Intuit sold directly by Amazon itself, since there's no way to be sure all third-party sellers on Amazon are legitimate. Here's a list of authorized retailers:
Be aware there are "too-good-to-be true" Internet scam sites selling fake or pirated software, or which may implant malware, steal personal info, etc. Only companies in the above FAQ are authorized for legit TurboTax downloads.
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 2019 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.
No, each year has its own forms. For doing 2019 see this FAQ