These are largely built on top of either a stream processing (in case of Flink) or some flavor of Actor model based on event sourcing for peristence.
What I'm getting at is that you'd build a serverless system on top of Elixir/Erlang/OTP and be served well by its mature actor model implementation and excellent distribution options. See https://eigr.io/ .
The cloud provided options are interesting for some experimental / tactical use cases but I don't yet trust their abstractions to not be leaky and they typically come with vendor lock-in trade offs.