@donald Can you check and make sure that the drive appears under /Volumes please?

In Disk Utility all drivenames are preceeded with \volume

@donald My question was meant to ask if you see the drives under /Volumes in APP.

Ah, no, in APP there is nothing more than just "\" and "users" and "Donald", "Donald" being the working folder. There is nothing on a higher level than "\".

@donald Just a side node. Unix and unix-like systems (like linux and macOS) don't have "\". They only have "/". In other words, the separator used is a forward slash. Only Windows uses backslashes. 

Having said that, what version of APP are you on?

Yes you are right "/". The version is 1.083.2 for Mac.

@donald Thanks for confirming the version of APP. I am not aware of any permission settings needed in the macOS settings to give APP permission to see external drives on Catalina. On Monterrey, can you check and verify that APP has the required permissions by clicking on the Apple logo to the upper left of the screen and selecting System Settings?

@wvreeven ? what do you mean?

Yo! Found it!

Go to the field: "Folder Name", delete whatever is in there and type: "/volumes".

Then the button for the file loader shows: "/volumes" and click on the button. Now the fileloader opens with all the drives.

Now that I have APP running I can tell that this volume changing is very poorly programmed. It is simply impossible to easily go through your drives and folders. My built in drives are slower than my Samsung T5 drives on a USB 3.1 port so I have quite some work in switching from the internal drive that holds all my images and the work drive outside.

@donald Unfortunately Java on macOS doesn't reveal which directories are mapped to external folders so this is the best we can do. Agreed though that it is a shortcoming but as long as macOS doesn't improve in this respect, it cannot be solved.