This is where I've found Astro to really shine. Most people reached for it because of the whole "islands of interactivity" concept, but IMO the ability to easily build a mostly static site with server APIs when needed is a the killer feature.

I manage multiple Astro sites and eventually they have all needed at least a few small server endpoints. Doing that with Astro is very simple and it can be done without making the static portions of the site a pain to maintain.