I think the codes are confusing, maybe they didn’t update the year for code P, but it worked once I answered the calendar year question. You can always enter it to see what it does and delete and start over.
I filled it in how my 1099-R was with a “P” and then TurboTax asked what calendar year, which mine was 2019. I knew it worked because it decreased my refund (since my taxable income increased).
The earnings on my distribution has a separate 1099-R and that one had a code 8, for calendar year 2019. This one did not change my taxable income and I’ll have to input it next year.
Note: I overcontributed to 401k for 2018, but the amount wasn’t taken out until this February (due date is by April 15th I believe). The 1099-R forms say 2019 since that was when it was distributed. The over contribution is taxable in 2018 but the earnings not until 2019.
