According to the Crucial homepage, compatible with "iMac (Retina 5K, 27-inch, 2019) iMac 19.1", but NOT compatible with "iMac (Retina 5K, 27-inch 3.0GHz Intel Core i5, 2019" - so it depends on your 2019 model (see
https://www.crucial.com/memory... and then test compatibility with your computer).
I have installed them in a 2020 model together with the original 2x4GB equipment, nerds will complain about a small performance loss (measurable with special devices), but in everyday life I did not notice it at all.
