I know, i am a very early OSX adapter: i installed OSX Mojave beta on an external drive.
Now, Just for people interested:
(For me) The install of Groove Agent 4 gives an install error, so fails to install on OSX Mojave Beta 3.
After this experience i didn’t even try to install Cubase Pro 9 
Ofcourse i am aware of the fact that Steini first has to make it’s products Mojave compatible.
Just wanted to try it, just wanted to share my experience.
Warm Regards.