Without a plugin or service? You can’t. There’s no such thing.
From the documentation for wp_get_shortlink() (emphasis mine):
This function exists to provide a shortlink tag that all themes and
plugins can target. A plugin must hook in to provide the actual
shortlinks. Default shortlink support is limited to providing ?p=
style links for posts. Plugins can short-circuit this function via the
‘pre_get_shortlink’ filter or filter the output via the
‘get_shortlink’ filter.