Xfinity gateways don’t tend to interfere with the Nucleus One’s network visiblity, so this is likely at the level of MacOS.
First off, it looks like RoonServer is still active on the Mac itself, which will prevent the Remote from connecting to the Nucleus. If you haven’t already, you’ll need to follow the steps here to create a Backup of the Mac-hosted RoonServer to prepare to migrate to the Nucleus.
If you’ve already secured a Backup of your database, take the following steps:
Close Roon Server in the background from the menu bar on the Mac (or using Activity Monitor in Applications → utitilies).
Navigate to your RoonServer’s Database Location on MacOS and delete the folder named “RoonServer.” Do not delete the folder named “Roon.” This will clear the database deeply from the machine, leaving only Roon Remote.
Next, navigate to MacOS System Settings → Privacy & Security → Local Network and toggle on access for Roon. Even if it’s already toggled on, toggle it off and on again.
Power on the Nucleus and open Roon on the Mac. You should see the option to select a different Roon Server if the Nucleus isn’t already listed. You can then restore your Backup as needed.
Please share a screenshot of what you see in step four if you’re still having issues. Thank you!