Technically, you may become a US resident for tax purposes for the year of 2019. ( filing season 2020) You cannot use TurboTax to file a nonresident return for the year of 2018. (the filing season 2019).
As a J-visa holder, you are considered as a nonresident for two years from the first year you entered the US. (2017 -2018). Starting from January 1, 2019, you may be treated as a US resident for tax purposes and file a Form 1040 if meet the Substantial Presence Test ( stay in the US for more than 183 days in 2019). However, during these two exempt years ( 2017-2018 being a nonresident), if you married a US citizen or resident, you can be treated as a US resident if your spouse files an election and you both will file jointly on a Form 1040. Please see Nonresident to resident
As TurboTax does not support nonresident filing, please see Sprintax for assistance.
