Nameserver doesnt work

If your domain has one of the extensions mentioned in the article, this is enforced at registry level and unfortunately nothing can be done.

If it’s a registrar restriction, then you can transfer the domain to another registrar, or try to lift the restriction.

I looked up Strato’s documentation and they seem to mention offering DNSSEC as part of their “Domain Guard” service, so disabling it from there should help: