How to access elements in a 'hidden new window'?

[Angel-Dzhambazov]

Let's have for example a public page like https://www.sixt-neuwagen.de/ when we first open it we see that a cookie window comes up. This window does not look generic at all and it's hard for me to navigate to its elements. Inside of it we see a shadow-root. How do we access this new window? Let's say for example, how do we accept the cookies for this website?