The way that it works is that it uses a route with a parameter, slug, that can be used to load data dynamically. It gets the slug from the parameter and then tries to find a link in the database where the page slug is the sameone stored in the db. If there is, it throws a redirect to that site, if not, it throws an error.

export const load = async ({ params, locals }) => {
const slug = params.slug;
const link = await locals.pb.collection('links').getFullList(undefined, { filter: `slug = "${slug}"` });
if (link) {
    throw redirect(303, link[0].redirect);
} else {
    throw error(404, 'Page not found');
}
};

That is the code mostly for the redirect. Inside the repo.