AFAIK this is not supported - the API always returns all related entities.
Maybe you could work around this using multiple requests where you first fetch all your Categories and then you fetch 10 articles for each. Roughly like this:
const categories = await request("/api/categories?pagination[pageSize]=999")
const articlesPerCategory = Promise.all(categories.map(category => {
return request(`/api/articles?filters[category]=${category.id}?pagination[pageSize]=10`)
}))
Not the most performant solution tough. ./