GraphQL custom resolver in V4

[gvocale]

I am trying to use this as described here Build Custom Resolvers with Strapi, but the query doesn’t shop up in /graphql

module.exports = {
  definition: `
    type Collection {
        title: String
    }
    `,
  query: `collectionBySlug(slug: String!): Collection`,
  type: {},
  resolver: {
    Query: {
      description: "Lorem ipsum",
      collectionBySlug: {
        async resolve(_, { slug }) {
          const entities = await strapi.entityService.findMany(
            "api::collection.collection",
            { filters: { slug } }
          );

          return entities[0] ?? null;
        },
      },
    },
  },
};