Stop Sync on icloud
I need to stop my MAC mini from syncing data to my other devices. It is inhibiting copying files from my MAC HD to an external drive.
Mac mini, macOS 15.1
I would check your settings for icloud to make sure that you don't have then enabled
System Settings-->Apple Account-->iCloud-->Drive and unenable them if they have been enabled. Also shut down Sync This Mac if you are not going to use iCloud. Also turn off any apps you don't want taking room up on iCloud in "See All".