If you purchased and paid for TurboTax 2018, in 2019, then if it qualifies it would be a deductible expense on your 2019 return. Remember, income & expenses are reported/taxable/deductible in the tax year the monetary transaction physically occured. It flat out does not matter what tax year the transaction may have been *for*.
But for most, since itemized deductions make absolutely no difference to your tax liability until the total of all of your itemzed deductions exceed your standard deducting, itemizing really makes no sense for more than 90% of your "typical" tax filers.
