Does it bother him that it's untidy? If not, can you just get a huge basket to toss everything into to hoover occasionally, and then at least it's quick?
If he is bothered by it, this might be a bit off-the-wall, but there is a YouTuber I really like called Clutterbug who talks about "organising styles" (e.g. some people like to put everything in its place, others in big buckets, some people like to be able to see everything, others like it hidden away).
It may be that he just doesn't care about things being tidy, but it could also be that he struggles with your organising style and something else could work better for his room?
I wouldn't show the videos to DS as they have "bits at the end" where she tells a story that is not always child-suitable
but might be worth you having a look and seeing if something different might work better for him? The lady who runs Clutterbug has ADHD so although it's not autism-specific at all, I think she just "gets" that different brains need different solutions.
Alternatively is there just too much stuff? Could you put any of it in the loft/storage and get it out in rotation?