From my experience the 2017 ***''4K''*** A1418 screens are compatible with the 2019 ***''4K''*** A2116 iMacs and vice versa. My parts distributor has the following in the description and I have not had any issues with compatibility as long as they are ***''4K''*** screens. The 2K screen from the 2017 a1418 ***IS NOT*** compatible with the 4K iMacs from 2017/2019 and vice versa.
* LCD Display for use with a 2017 A1418 and 2019 A2116 21.5" ***''4K''*** iMac.
* Model Number LM215UH1 (SD) (B1).