The Issue
macOS Sequoia (version 15), has tighter (and more obfuscated) network security settings than preceding macOS versions.
This is causing problems during Roon updates; despite being previously enabled during the Roon installation MacOS, after an update MacOS is denying access to the network (yet retains displaying all is well).
Roon Status
Roon support and product team are aware and are working a fix, which I understand is quite involved (I have no timeline for that, sorry).
The Workaround
Please navigate to macOS System Settings > Privacy & Security > Local Network, and make sure Roon is allowed.
If it is already enabled, toggle the setting off and on again. Then reboot your Mac, and see if the same issue persists.
I hope it helps, if not please follow this link to provide specific details of your case to Technical Support.