I currently have a MacMini late 2014 with OS 10.15.7 I have a 1 Gig USB SSD attached to this computer and my Roon core, backups and music are on this USB.
I would like to move my Roon core to the hard drive on my MacMini and keep my music files on the SSD.
This would be a bad idea. The Roon database requires the performance of an SSD to run well. Putting it on a lower-performance HDD is likely to end in tears.