Current versions of macOS Server are a package that is best suited for managing devices; an MDM package.
Older versions of Server.app provided mail, chat server, networking, DNS and other network services, though those and other capabilities have been deprecated and are no longer available in the version of Server.app for Mojave, and a few—such as file services—have been migrated into the base macOS distribution.
Typical server boxes now are either hosted services (Amazon, AWS, etc) or hosted systems (Scaleway, Rackspace, Linode, etc)—for those that want or need to maintain their own servers—are running on Linux, BSD or Windows Server configurations and usually on x86-64 or Arm servers.
There are folks that do use macOS—without Server.app—as a server, and one hosting provider is macminicolo. There are some others.
If you're aiming for less management, you're probably going to be installing and booting on an x86-64 or Arm server packaged with whatever operating system distribution might be necessary, and that either booting natively or as a guest in one of the common virtual machines.
But without some specifics on the plan and the requirements, there's little that can be specifically discussed.