What they mean is that instead of using "serverless" hosting running a rust program to generate ics files you could literally just have a statically hosted html file that uses a couple lines of javascript to generate the ics files within the browser, so there would be no rust or server component at all.
You could just host it with github pages.
Actually I'm confused why you're saying:
> The Rust part is just for the routing
Because it appears that you're generating the ics files in rust?