Hi - I have Roon hosted on a Mac Mini (remote on MacbookAir) but since installing Roon the MacMini has stopped going to sleep. I would expect it to go to sleep after the time set in Energy Saver when Roon stops playing music.
I’m going to take an educated guess that the Roon installation that is designated as a Core is running a Server process. As such, whether or not you are playing music from your remote, the Server process is still active at all times because it needs to be “awake” to accept and process the next request.
Try turning off Roon on the Mac Mini and see if it goes to sleep.