can I file my 2018 return?

TurboTax does not support tax year 2018.

If you file a 2018 tax return with a tax refund, the refund will not be paid since it is beyond 3 years from the due date of the 2018 tax return.

You should seek out a local tax professional to assist you in completing the 2018 tax return.

TurboTax no longer provides software for 2018; any refund for a 2018 tax return was forfeited several years ago and would not be paid to you.   If you owe tax due for that year, it is owed with late filing penalties and interest.  You could seek local paid tax help to prepare a 2018 return.