The way you phrased the question probably confused them.
Mojave supports HDR in Quicktime. You can download videos from 4kmedia.org and try yourself. The support is really good and better than Windows.
The macOS interface doesn't need HDR support. macOS is very clever by separating the user color profile for the interface and a HDR color profile for the HDR content. Windows can't do that. If you enable HDR on Windows it ****s up the system interface color profile.
Mojave doesn't support HDR for iTunes movies but Catalina does in the new TV app.