AppEngine isn’t serverless imho. You pay for instances, which effectively means that if you run one query, you are guaranteed to pay for idle, which is by definition *not* on demand payment and so therefore breaks one of the key ideas of serverless e.g. if nobody is using it, it costs you nothing.
App Engine Pricing | App Engine Documentation | Google Cloud
Some countries tax App Engine fees. If taxes apply in your country of residence, your bill will include any applicable…
We’ve had presentation, logic, queues, data etc on-prem for 40 years, so I don’t think you can claim that Google AppEngine is the height of serverless.