Thanks for your reply. But this happened after I completely erased my HD, reinstalled High-Sierra, and restored my files from a back-up—three times! In the process, various file issues developed (privilege issues, missing files, etc.), all of which I "fixed" by repeating the above re-installation regime with the help of Senior Apple Support Techs. Besides the problem here, I now have my photos in two Photo Libraries, which I need to merge. Needless to say, nothing I do can cause any loss of my user information (photos, music, books, etc.). I'm hoping someone knows where the missing folder is and how to restore it without a complete system redo.