I've notice recently that Roon continues to play music even after I've closed the software on my iMac running Sonoma 14.5 I also have to trick sometimes Audio Midi Setup to connect to my Denafrips IRIS to hear music through my headphone setup. These are all recent issues.
Describe your network setup
I'm plugged directly (USB) from my iMac into the Denafrips Iris -Denafrips Pontus II - McIntosh MHA100
There are three elements to Roon: Server, Roon Desktop/Remote and endpoint.
Closing the Roon Desktop or Roon Remote does not stop the playing of music queued on an endpoint (other than an endpoint integrated into the Roon desktop or Roon Remote applications).
Closing the Roon Server application (wherever it is running) will stop all music playing.
Shutting down an endpoint (including those integrated into Roon Desktop or Remote) will stop the music playing on that endpoint.