macOS 10.14 Mojave is due to be released on September 24.
At this stage it is not supported by any version of DIVA.
It is also unlikely, looking at previously releases, that Avid will support it out of the gate. From testing the Mojave betas with Media Composer, I would also expect this to be true.
We’re working hard to update DIVA Client to provide Mojave support, and hope to have something available before the end of the year.