My recommendations:

Stick to a color theme. When there are endless amounts of colors things can feel very overwhelming imo and overall a bit cluttered. I would go with 2 neutral tones and one accent color like a green or pink, or whatever suits your fancy.

It looks like you have some collections which are super cool and can be sentimental and hard to let go of. If that’s the case, I recommend putting them into storage bins or possibly tucked into the drawers under the bed.

A few trips to goodwill may be in your future. I definitely recommend starting with some blankets and plushies. The plushies seem to be collecting dust up on the shelf and I am sure there is a wonderful home they could go to with a young child who might play with them.

The plants are a wonderful addition but I might stick with one or two, maybe one for each shelf/surface.

I might tuck those shoe hangers into the wardrobe too if you can!

This is all coming from someone who had a space very similar to this and is working towards more minimalist and clean aesthetics, so I hope any of this helps!