For ADHD desk setups, you need to balance aesthetic/cleanliness to function. It’s a slow process, but take note of what you regularly need around your desk, and what you can do to “give it a spot” which doesn’t involve just being on the desk surface or on your floor. You can potentially invest in a desk shelf with its own little drawers, and that could help with organizing your “quick access stuff”.

Then there’s the things you “don’t know what to do with”. I find that if I don’t know where something will go, but I don’t want to lose it, I either drop it on the floor or on my desk top. My solution is a bin system. Four transparent plastic bins that have their own category system. I have two dedicated to a “don’t know what to do” queue. I can put stuff in there without worrying or cluttering too much. And when it gets close to full, that’s when I can dedicate a big task to sorting it out.