In your example, the mistake was requesting a distribution that was adjusted for investment loss. After the due date of the 2018 tax return, a 2018 excess contribution can only be eliminated by making a regular distribution (code J) of the entire amount of the excess or by applying that excess as an eligible contribution for a subsequent year.
In your example, only $800 of the $1,000 was distributed and TurboTax is correctly reporting that $200 of the 2018 excess still remains in the Roth IRAs (unless the balance in all Roth IRAs was zero at the end of 2020 which you would indicate to TurboTax by saying that no Roth IRAs were "open" at the end of 2020). Since 2020 has passed, that $200 will need to be distributed as a regular distribution in 2021 to eliminate the remaining excess on the 2021 Form 5329.
