I think you need to set a UID field on the repeatable documents you're trying to fetch in Prismic as this is what you're trying to get. The second param of getByUID is expecting the UID of the document which it can't find. Slug is no longer recommended
In addition to the above you can also change your file name from [slug] to [uid] for good consistency with the Prismic eco system.
Then see if it works by:
const { data: proyecto } = await useAsyncData(route.params.uid, () => client.getByUID('proyecto', route.params.uid))