This particular case, with the numbers given, would work as a server for profile pictures, for instance. Or for package signatures. Or for status pages of a bun

This particular case, with the numbers given, would work as a server for profile pictures, for instance. Or for package signatures. Or for status pages of a bunch of services (generated statically, since the status rarely changes). Yes, an RPi4 might be adequate to serve 20k of client requests in parallel, without crashing or breaking too much sweat. You usually want to plan for 5%-10% of this load as a norm if you care about tail latency. But a 20K spike should not kill it.