If you received your 2019 RMD in 2020, you will report it on your 2020 tax return, not on your 2019 tax return. For an RMD that you received in 2020, you will get a 1099-R after the end of 2020 (or it will be included in a 1099-R along with any other distributions that you take in 2020). This is true even if the RMD that you received in 2020 is for 2019.
