I'll load the save and have a look. Hopefully no new bugs have materialised.
Okay, first of all it seems you can't donate items from your inventory full stop.
Some of the things in the house that my sim can donate include: the umbrella rack from Seasons, her TV, gaming console, grill, "eat the plank" table (but not her other dining tables), patio chic coffee table, massage chair, microwave, her expensive trash can, sinks, schmapple fridge, throwback stove, toddler bookcase, Uni (one of the interactive stuffed animals), toybox, the kid's chemistry set, all the mirrors in her house, baths, showers, toilet, flower arranging table, tea maker, espresso set, lights, stereo, digiRAD keyboard, massage table, computer, meditation stool, all fitness equipment, microphone, 2 of her countertops in corners (but there's another she can't donate for some reason). And probably others.
The major categories she always seems able to donate are electronics, appliances, plumbing, some skill items, some children's skill items.
She can never donate chairs. She can't donate the chess set. She doesn't seem able to donate any of the media production items.
I hope this helps. If you try to donate and can't get any of these to work, double-check you've got the perk. If you do, you might have a bug and need to try repairing your game or something.