Let me start over. Youtube itself has DRM required for certain videos, and certain formats of videos.
The 256 kbps format for music will be protected by DRM. If you do not have DRM available youtube will fallback to a lower quality format to play the auduo.
Music might have higher quality audio-only files as provided where Youtube might have it combined with video and a generic compression algorithm applied as with all other uploaded videos.
If it's on YouTube Music, it's also on... YouTube.
Not necessarily at the same quality though.
I assume in most cases they're literally the same files. Youtube runs "topic" channels for music that distributors have sent it.
https://www.youtube.com/channel/UCYOa-hi751OKY2zGJJv6V2A
https://www.youtube.com/watch?v=MSSxnv1_J2g (same thing, but on an official channel instead)
You can load any youtube music song on youtube by just removing the "music" subdomain.
Then why do you say they might not be the same files?
Let me start over. Youtube itself has DRM required for certain videos, and certain formats of videos.
The 256 kbps format for music will be protected by DRM. If you do not have DRM available youtube will fallback to a lower quality format to play the auduo.
Music might have higher quality audio-only files as provided where Youtube might have it combined with video and a generic compression algorithm applied as with all other uploaded videos.