Did you enable the BF Pro as a sound input in System preferences/Security & privacy?
That's new in Mojave and a lot of people get bitten by it. Before you just needed System preferences/Sound and Utilities/Audio and MIDI setup. Now there's a third location to check.
EDIT: older RME drivers are available. I just change the number in the download URL. That works. There's also a link for them somewhere on that page, but it's not obvious. I downloaded a very old one for my G5 recently