@k4v thanks so much for your answer.

Well, I try to avoid base themes and try to write my own theme which only relies on the bootstrap 5 framework directly. All the themes relating to bs5 have a massive configuration overhead in theme settings, which makes everything bloated up 🙂 (barrio, radix etc. ). But haven't found a really clean/lean theme yet where I just can modify the twig templates/SDC and maybe some css/sass variables without relying on a base theme