- ensure that your poster files conform to the supported naming scheme https://support.plex.tv/articles/200220677-local-media-assets-movies/
- configure your library to actually use local poster art, by enabling “Use local assets” in the properties of the library
- Reset all manual poster selections in a library at once or unlock other metadata fields
- “scan library files” – wait until completion
- “Refresh Metadata” on the library level
