Hello @BryonyRae
Apparently this is by design, for performance reasons.
Specific objects, when placed indoors with indoor lighting, are not affected properly by the indoor lighting. I do not have a comprehensive list, but some examples are included in the screenshots. I duplicated the room to show the same set of objects: the room on the left lit properly, in outdoor light, and the room on the right with indoor lighting and the objects in shadow.
You can tell which objects are affected because when you click/select them, they have the proper lighting, which dims when they are placed down. When you hover over the placed object, the shadowed items also do not get the usual perimeter highlight that items get. Most of the items with this bug are in the 'indoor plants' B/B category.
This has been called as By Design for performance reasons in the past: [BY DESIGN] Wall Sculptures and Plants darkened in the Interior | EA Forums - 8550242
It is something that gets reported quite often though.
dang, that's frustrating, especially for items labelled specifically for indoor use - thanks for letting me know
