I have installed the latest version of macOS (10.14) as well as the latest version of Roon (1.5). If I press the play/pause, next or previous track buttons on the keyboard of the Mac while Roon is started and playing music, nothing happens. If I press the play/pause button Itunes starts.
If you had bothered to read the release notes for the latest update you would have come across
“macOS Mojave changed some details about how permissions work. If you would like to continue using media keys on your keyboard to control Roon, you’ll need to click Grant Permissions on the Setup tab in Settings. Note that this step is now required even on older versions of macOS.”
I dont mean to be condescending but when installing an update one really should read the release notes, especially when it appears the update “breaks” something. I dont even use a Mac.