I’ve been trying to wrap my head around this whole agent thing for the past few days now. I’ve tried every combination, and my artworks always look terrible. What I don’t understand is that the default artworks (posters/backdrops), on TMDb look awesome, but when I try adding TMDb to the top of my agent, the posters are still not the same as the ones on their site. My file naming convention is as desired, so that shouldn’t be the problem.
Careful: this won’t change any of the movies you already have in your library.
They’ll continue to be linked to the Plex Movie agent.
I also doubt that TheMovieDatabase has higher quality posters than the default ‘Plex Movie’ agent.
I think your real problem might be the use of m4v files. Those have embedded posters (as you can see by their file icons).
Though your screenshot shows that you have moved the ‘Local Media Assets’ below of TMDB, it is not clear when you did that. Before you did it, all those movies simply got the embedded version of the poster used in Plex.
Make sure to move the ‘Local Media Assets’ downwards under
Settings - Server - Agents - Movies - Plex Movie
as well.