The Site app is installed by the Site module.
The app is configured in
The Site app is actually a shortcut that displays the configuration from either the site module or multisite module.
config:/modules/multisite/config/sitesin a multisite setup (DX Core) each site has a parent node. This gives the site a name, such as, fallback, travel or sportstation. Each of those sites can have a separate Site configuration.
In DX Core one or more site definitions are possible. Each definition will have a name and a configuration node.
The Site module operates on