Hi Alex,
- To access the component library on your site via Site administration > Development, you first need to build the component library on your machine, as described in the dev doc https://moodledev.io/general/development/tools/component-library#building-the-component-library
- There is no need to log in if you just want to browse the component library online on the site componentlibrary.moodle.com. (The 'Log in' link is confusing though; it would be good if we could hide it.)