So, there is no way to these copy files off that I can see what I open up a folder under Linux MINT on my linux desktop computer?
Linux might be a CLI system, but there seems to be a GUI that people use. A simple copy command should be executable form a GUI. Unfortunate that it is not.
You can either try with the gui, or do it right the first time. The choice is yours. I’ve been at this a long long time.
Since your question also involves putting your Plex metadata on an external HD,
you have the burden of additional steps; none of which can be done in a gui.