Take a look at this post – it goes through how to grant full disk access for Roon. My guess, as you’ve already confirmed that this isn’t a permissions problem with the hard drive, is that your Mac ‘forgot’ that it had access to this folder when you updated Roon.
EDIT: If System Preferences shows that Roon does have ‘Full Disk Access’, click on Roon in the list, then the minus button just below the list. This will remove Roon from the list. Once you’ve done this, click the plus button and add Roon again.