I don't understand. Compatibility is announced by Apple https://www.apple.com/macos/catalina/features/
However, Macworld has written something else https://www.macworld.com/article/3444585/8-hidden-features-of-macos-catalina.html4K, 4K HDR, 4K Dolby Vision, Dolby Atmos, and HDR10 content is available on all Mac models introduced in 2018 or later with 4K-resolution screens.
As for full-on 4K HDR streaming, it’s enabled only on 2018 and later MacBook Pros and 2017 and later iMacs with the T2 chip. Unfortunately, that means that older 4K and 5K iMacs are out of luck.