When I try to use the Roon display feature (following these instructions) I only see the Roon logo. Here is my setup:
Roon Core on mac mini, wired to router
Roon Display in Safari/Chrome on Macbook Pro (wifi)
From Roon, I go to Settings > Displays and it says “No Available Displays”. I copy and paste the URL to Safari or Chrome and it shows just the Roon logo. The Roon Player still says “No Available Displays”
It sounds like you might have a firewall active if there are no displays showing up under Settings -> Displays. Please use these instructions from Apple to verify that Roon is listed as an exception. I would also temporarily disable and Antivirus or Firewall blocking software and make sure that Chrome on the Macbook Pro is up to date.