So basically, you used a metadata attribute in iTunes for a different purpose.
This attribute is however not supported / available in Plex. Hence you can’t filter for your custom moods.
There’s a number of feature suggestions with regards to Plex supporting that particular attribute [1][2] – that being said, not sure if it’ll help you as you’re not using it for the composer but to reflect some custom categorization.
If you don’t care for the Mood/Style information in Plex, you could try to transfer your custom Composer values to one of those. I don’t have a tool at hand, but I’m sure there’s some scripts that’ll do that.
Feature Suggestion: Filter by Composer ↩︎
Feature Suggestion: Wider native support for embedded metadata ↩︎
