3 Themes generated when installing SASS Starter kit

Hello, I've been using this theme since 2019 on multiple sites. It has come time where I am beginning a new site. What is confusing me is, after installing the theme via composer, why do I see 3 different themes in my drupal appearance menu?

I see
themes/contrib/bootstrap_barrio
and
themes/contrib/boostrap_sass

Then inside bootstrap_barrio there is a subtheme folder, but also the bootstrap_sass folder references the bootstrap_barrio project when it builds scss styles. Why cross reference from one theme to another? Is the sass starterkit not self contained? Which theme do I select in the appearance menu as the default theme? And which theme or where should I develop my sites theme, and in what way do I utilize the SASS starterkit?

Thanks