I have the same problem with an attached Raid array. I used to have access just fine, but now get the message:
This directory appears to be empty.
Add some files or edit this folder if it’s been moved.
I’m not sure either, I suspect the last Roon update because I think that was the most recent change. My Mac mini recognizes the WD external drive and all of its contents. It is the Roon core that cannot see the files and reads the drive as empty.
My symptoms are exactly the same. I am on an iMac (2020 with Intel i9). The external drive is a Promise Pegasus 2 R4 Raid array and it is mac formatted. I wonder if we un-install and re-install Roon if that might fix? Other ideas?
I need to be sure that nothing will happen to my files when I uninstall Roon. I have all of them backed up on a second external drive so I suppose it might be worth trying that. I have also thought about purchasing a new external drive and seeing if that might work with Roon. I am pretty sure this problem started with the last Roon update - and there was another one today - and not with Monterey which has not given me any problems so far.
I discovered that in addition to authorizing file access to roon, you need to authorize “full disc access” in the privacy settings. Not sure if this is a new requirement or if one of the updates switched it off, but it is now working form me. LMK if you need more details.