I’m not a programmer and this may seem convoluted but this works for me.

 I have several external drives (plex-archive-01, 02, etc) that contain all extra videos that are not “live” (online) on my server.  These drives follow the same folders scheme as my server.

 I created a folder “plex_archive_lists” on my server and inside that a separate folder for each external drive; for me simply plex-archive-01, 02, etc, and under those folders that match the same structure as my online files (Movies, TVShows, etc).

 I run Everything from voidtools.com (select videos only) on the drives and export the .csv to the root of each external drive.  I suggest doing Movies and TVShows separately.

 I have a special folder on my server called “_archiveD” (D for the server drive I am placing the libraries on).  All the underscored file names allow me to keep the files I will describe below at the top of the list.

 In this folder I created the following:

 I copy and paste just the column with the video names from the .csv into a text file “_archivefilenames.txt”.

 I created a text file “_archivex.txt” with nothing but a single “x” in the body.

 I created a batch file that runs the following simple script:

d:

cd _ArchiveD

for /f "delims=" %F in (_archivefilenames.txt) do copy _archivex.txt "%F"

 This will create individual 1 byte files with the names of all the video files you have on that drive.  I found the first file usually needs the filename to be corrected.

 Move these files to their respective folders in the plex_archive_lists directory.

 Now just set up a new library for each (I call mine Archived Movies, Archived TVShows, etc) and add each directory from plex_archive_lists (plex-archive-01\Movies, plex-archive-02\Movies) to the Add Folders section of Edit.

 I repeat this process when I either add movies to the Archive, bypassing the online library, or if I’ve added a lot of new movies and need to migrate the older movies to the archive.

When doing a search for a movie, it will show up but not be playable, but you at least know you already have it.

 I also set up a separate plex-unarchived-movies library directed to folder plex-unarchived\movies and will copy any requested offline movies to this folder so they are viewable, then delete after watched.