My just turned 12 daughter is a collector of things (paper, craft supplies, letters, cards, toys…) It is her, but not me. I am a minimalist by nature so her room makes me nuts, haha.
What we have found works is she has shoe boxes on shelves. Shoe box for letters, papers, craft supplies… when those boxes get full, time to sort and toss (or give away). The shelves also help because it limits space, so she can only keep so much when new things come into her room. I sort with her, we sit down together talk about items, why she wants to keep (the value of each) and over time, and practice, she is getting good at it and it is no longer a stressful experience. She now gladly gives thingd away and no longer feels the need to keep every little piece of paper with a note on it. We do it every couple of months.
Now my brother growing up just would not put things away, even his closthes. It got to the point he had very little in his room, he did not care as he was not a collector or toy kid, and the only solution he would do was a basket for clean clothes and a basket for dirty. He rarely used his drawers but his odd system worked for him and his room was not messy any more. My mom let it go at that and no longer nagged, haha.
My daughters room will always be “messy” to me but over all she is pretty tidy and her system works so that she feels in control and I don’t feel overwhelmed by the stuff. She is also learning life skills of not keeping everything but keeping what is used and some special things, but not everything is special 🙂 Also the gift of giving to others who will appreciate and use the items.