Well in the JAMstack a database (or any other datasource) can be used and required during the build step, which will generate the static html using that datasou

Well in the JAMstack a database (or any other datasource) can be used and required during the build step, which will generate the static html using that datasource (see getInitialProps in nextJS). Once the static html is generated and output, the datasource is not needed anymore. This is pretty much in contrast to other stacks, where more often you will not need a database at compile time, but only at runtime. Of course, the statically generated HTML will not update unless rebuild and deployed (except if you use a hybrid static/dynamic approach using Javascript or the completely server-side rendered mode, both of which are also supported by nextjs).