should i self-declare a post-tax IRA contribution if my bank did not provide a 1099-R?
You'd receive a 1099-R only if you had a distribution, rollover, conversion, or recharacterization of an IRA.
I'm assuming that you contributed to a Roth IRA, correct? You do want to enter that into your TurboTax program, just for record-keeping purposes. See the instructions in the TurboTax FAQ below for entering this 2018 contribution made in 2019.