I had many private files before I moved them from internal storage on my 10.5 Tab S to my SD card. Can I hide files or the entire SD card or can they only be made private while on internal storage?
Any file with a dot as the first character of the name isn't visible to the phone, unless the app is told to show hidden files. Since 4.4, the SD card is part f the file system, so whatever applies to internal storage applies to the SD card as well (except that Android isn't designed to run apps from either SD card, the internal one or the external one).