How is the Liberty II connected? We would expect it to be plugged into the Mac Mini by USB, but please confirm, since Mytek make network streamers as well as USB DACs.
Where is your Roon Server running, and what is installed on the Mac Mini? The server can be the Mac Mini itself or any other machine on your network. The Mac Mini only needs Roon, Roon Bridge or Roon Server on it, any one of the three, for the Mytek to appear as an audio device.
If it is USB into the Mac Mini and Roon Server is running there, the rest is two steps:
Open Settings > Audio. The Mytek should appear in the list of connected devices. Please click Enable next to it and give it a name.
TIDAL then appears in the sidebar, and anything you play can be sent to the Mytek zone.
This article covers the wider setup if you want the full picture:
If the Mytek does not appear under Settings > Audio, please try the following steps:
Open macOS System Settings → Privacy & Security → Local Network
Make sure Roon and Roon Server are both enabled
Even if they are already enabled, please toggle them off and back on
Fully quit Roon Server from the macOS menu bar / task bar
Reboot your Mac
After reboot, launch Roon again and check if the devices is avaliable again.
Once these permissions are refreshed and the system restarted, your audio devices should reappear.
Please let us know if the issue persists after these steps, and we’ll continue from there.