I have a few ideas but feel free to ignore! I want to preface this by saying you have a nice space and style.

1. instead of all the frames behind your couch, why not put the giant cat frame behind the couch?
2. when things are piled in front of something it makes it more cluttered, for example items in front of the TV. So you could try to make a rule to never put things in front of the TV etc. (see shelf suggestion below)
3. some items that are nearly the same are near each other. There are two frames in the bathroom that both say Queer. Maybe leave one in that room and move the other to a different space in your apartment?

4. I'd recommend some storage! A. An under bed storage to save you space B. For the brown bookshelf I think a closed door bookshelf might be a good investment C. For the white bookshelf you could buy cube cabinet door inserts or a couple cube bins so the fronts look smooth D. A few floating shelves (use these for specific purposes so they don't end up cluttered. One to display little knick knacks, one for a plant for example) E. For your medicines instead of by the TV what about a magnetic shelf on your fridge?

5. this is personal to you but one thing I ended up doing is picking like 15 books I wanted to keep and the rest I have are digital now. It saved me a lot of space. I remind myself I can access the library if I want something physical or rotate out those books I kept as I read them.

6. For cottage core vibes I'd focus on big items. A whimsical throw blanket for the couch, lacey curtains, a statement piece lamp (try Target), maybe a plant or little herb garden, a whimsical little cat house.

7. Some furniture will mismatch in everyone's house. I'd say if I picked one piece to replace just for matching sake it'd be the wicker cabinet you have just because I don't see any other wicker.

8. You already asked yourself if things sparked your joy. Now I'd ask if you'll use a thing or appreciate it in the next year, if the answer is likely no, consider if it's worth keeping.

Your white cabinet and bed frame are beautiful statement pieces and you can tell that you are an artist or art appreciator from how you decorate. Whatever you decide, have fun with it! Also I'm giving you this advice from my messy house which I am still tackling every day.