Thank you very much for your reply and explanation.
Based on what you wrote I've done some follow-up reading and observing, and now I better understand the situation. I apologize for assuming and incorrectly stating that those file "._' files were generated by Rockbox.
I use Windows for formatting my iPods in iTunes, and also for installing/updating Rockbox. For all other things - most prominently for managing my music library - I use macOS. I know about the showing and hiding of invisible files on the Mac, and I often intentionally show hidden files. When I connect my iPod to my Mac and show hidden files I still don't see the "._" files even though they are there - it's the Mac that is creating a 'virtual' unified file kind of state for those files on the iPod's non Mac volume. In Windows I see that those files are hidden unless I check the Hidden Items checkbox.
So would it be possible for Rockbox to have a Show Files setting that would allow the user to choose Show or Hide for invisible files?
In lieu of that, my immediate solution for my 'problem' will be to select the Supported setting under Show Files, and add Show Files to my shortcuts so that I can quickly switch to All when necessary. But I would love to be able to just hide the invisible files while keeping all other files, both supported and unsupported, visible.
Again, thanks.