Yeah this is actually quite nefarious, as it is a private organization that decides what sites get blocked, with no legal oversight.

- https://de.wikipedia.org/wiki/Clearingstelle_Urheberrecht_im...

- https://netzpolitik.org/2024/cuii-liste-diese-websites-sperr...

Its a DNS based block, so overriding your default DNS server is enough to circumvent it. I think Dns over Https also works.