What Linux distros do? The comments in the `command` script on macOS indicate that FreeBSD included a separate executable for `command` in 2005. But there's no package in all of Nixpkgs providing a `command` executable and the command-not-found handler for Ubuntu doesn't suggest anything either.

The norm, afaict, is for `command` to be a shell built-in only, and not available as a separate program.