> I think your information is outdated. Java has had lightweight threads for several releases now.

Well, yes. It was released as a part of JDK 21 a year ago. So far, the adoption has been spotty. They are also implemented not in the best possible way.

> Xmx is mostly a thing if you have very small RAM, or some sort of grievously misconfigured container setup. By default it grow up to 25% of the system RAM, which is a relatively sane default.

Other more sane runtimes (like Go) do not even have developers care about the heap sizing. It just works.