I've been playing around with Alfresco for a while and I always use /alfresco/s/index for exploring Alfresco API which lists the content from /alfresco/s/api/.
Sometimes, when I use Docker, there is also a nice-looking Alfresco API Explorer (Swagger UI), but it lists a bit different (extended?) API - /alfresco/api/-default-/public/alfresco/versions/1/.
But if it is only the explorer, why the "extended API" is not available while API Explorer is not installed?