I attempted to implement the schedule trigger [1] on GitHub Actions as an example, but it is not being triggered as I expected. It needs more digging if you're so inclined.
Aside from that, the whole gist is that the initial data can be injected into the static files during the build step, or even saved as separate JSON files that the app can load instead of reaching out to the API. As long as you're willing to refresh the static data from time to time, of course.
I created a basic example at https://schedbuild.pages.dev/ with a rough, manual implementation of a build step. Frameworks like Next.js offer a more sophisticated approach that can render the entire HTML, allowing users to load the static page with the initial data already rendered without Javascript, and subsequent interactions taking over from there more seamlessly.
If the Github Actions schedule feature is ever sorted out, in my opinion it's a reasonable alternative to setting up a backend just for this.
[1] https://docs.github.com/en/actions/writing-workflows/choosin...