Automator "Copy Finder item" failing to writing to external WD hard drive

Hi all,

I was trying to create a Quick Action with Automator to copy one image file from a folder on an external hard drive, to another folder on the same external drive. I use the 'Copy Finder Items' action to do so. When I try it, it raise an error (see picture below):

Following suggestions on other posts, I already gave all the write & read permissions to all users, also including the Admin user (which seems to be the Automator user), on all the folders and files on the hard drive. I also enabled Automator to "Full Disk Access" via the Security & Privacy settings.

Funnily enough, if I run the workflow from Automator, it works (see image below), and I get the expected results.

While when I call it from the pop-up menu (see below), it fails and I get the aforementioned message.

The part that seems failing is the writing part. If I try to run the same action when changing the destination folder to a folder on my mac, it works. I tried to have a look in the system logs, but couldn't find anything useful. Any clue?

The external HD I'm writing to is a Western Digital My Passport for Mac 4TB 33178.

Thanks in advance