2016, 2017, & 2018 can currently be efiled.

The IRS shuts down efiling in mid-late November; reopens in Jaunary.  After that, 2016 can't be efiled, but 2017, 2018, and 2019 can be.

I don't speak PTO, but in Lacerte (PTO's big sister) you "turn off" efiling in the client screen by un-checking the box.