Interesting. A Spring Boot webapp (with the runtime dependency injection framework, etc. etc.) serving some static content and exposing some REST endpoints works fine with 32 MB RAM. Is it really orders of magnitude more than other languages, e.g. will a Go-based webapp consume less than 300 kBytes of RAM?

That's almost always a consequence of poor engineering. You need to consider the runtime when developing any program. With Java, that runtime is more than just your CPU and OS, it's the JVM too.

Forgot that our computers were so resource constrained these days...