use loading.tsx
https://nextjs.org/docs/app/building-your-application/routing/loading-ui-and-streaming

Note that if the page is static you probably would rather just send the page, setting up a loading page will trigger streaming so the page won't render with JS disabled for instance

it's more relevant for dynamic page where the server data fetching/render may take some time

if the page is static generated, next will serve the html instead