Not knowing anything about the new /app directory support, I'm able to migrate my static landing page in about two hours. The resulting page is definitely small

Not knowing anything about the new /app directory support, I'm able to migrate my static landing page in about two hours. The resulting page is definitely smaller and load faster than the previous version. Now I'm consistently getting 100 on page speed insight (mobile) while previously it's hovering around 98-99. The documentation for the new /app directory support is not complete though. API routes seems to be not documented yet (or is it not implemented yet?) so I haven't ported mine and leave it on the /pages/api directory for now.