A "static site" implies HTML rather than a JavaScript app.
With respect to JavaScript apps (React, Angular, etc.):
It's not clear these days because the major search engines don't explicitly clarify whether they parse JavaScript apps (or if they only parse high-ranking JS apps/sites. But 10 years ago it was a must-have to be indexed.
One theory on pre-rendering is it reduces cost for the crawlers since they don't need to spend 1-3s of CPU time pre-rendering your site. And by reducing costs, it may increase chances of being indexed or higher rank.
My hunch is that long-term, pre-rendering is not necessary for getting indexed. But it is typically still necessary for URL unfurls (link previews) for various social media and chat apps.
With respect to JavaScript apps (React, Angular, etc.):
It's not clear these days because the major search engines don't explicitly clarify whether they parse JavaScript apps (or if they only parse high-ranking JS apps/sites. But 10 years ago it was a must-have to be indexed.
One theory on pre-rendering is it reduces cost for the crawlers since they don't need to spend 1-3s of CPU time pre-rendering your site. And by reducing costs, it may increase chances of being indexed or higher rank.
My hunch is that long-term, pre-rendering is not necessary for getting indexed. But it is typically still necessary for URL unfurls (link previews) for various social media and chat apps.
disclosure: I operate https://headless-render-api.com