Official comment
For starters, if you only have TRIAL, that means you haven't activated a rekordbox dj license; EXPORT mode is the default.
And the reason you can't see your export device is you haven't given rekordbox permission to access removable devices. Open System Preferences > Security & Privacy > Privacy, and on the left select Files & Folders, then on the right, tick the box under rekordbox for Removable devices. If it's not listed, click the + icon to add it.
Note that you may need to click the lock icon at the bottom left and enter your password to make changes on this page.