Hello jav-it I use Plex as well, they have some good documentation about setting up local metadata if you want to have a look.
https://support.plex.tv/articles/200220677-local-media-assets-movies/
https://support.plex.tv/articles/local-files-for-trailers-and-extras/
if Kodi and Plex have different file structure maybe an option can be made to pick what one to use Kodi or Plex?