Using only a pattern or a material for the trim item component in a predicate returns No key pattern in MapLike or more specifically:

[00:19:39] [Worker-Main-58/ERROR]: Couldn't parse element predicates:spells:boots/trim_material_diamond - Not a json array: {"condition":"minecraft:entity_properties","entity":"this","predicate":{"equipment":{"feet":{"components":{"minecraft:trim":{"material":"minecraft:diamond"}}}}}}; No key pattern in MapLike[{"material":"minecraft:diamond"}] missed input: {"minecraft:trim":{"material":"minecraft:diamond"}}

While trims can only occur as a pattern + material, testing for only one of these is totally valid. For now I had to fallback to matching nbt in a target selector to archive this.
Ideally there would be a way to check pattern and material of the trim item component independently via predicates.