I believe I have the same problem, and it really bugs me! I use the "Computers" app to play music from my mac mini iTunes (home sharing).
I have always had the ATV setting "Screensaver-->Show during Music and Podcasts" set to "no". In the past, this has always worked nicely, and I could play music for hours. I'm now on tvOS 17.0, and the screensaver does appear while playing music! Much worse, after 1/2 hour, the ATV appears to go into sleep mode, abruptly cutting off the music. Grrrrrr!
My ATV "Sleep After" setting is 30 minutes. I assume this is intended to mean 30 minutes of inactivity.
I suspect there's a bug, and current tvOS versions count music playing as "inactivity" and go to sleep, whereas older tvOS versions didn't. That would explain why the screensaver comes one, in spite of the setting indicating it shouldn't.