Yes, that info (my answer from 2023) is now outdated. Changing the NS records in subdomains of dedyn.io is no longer allowed. Please read dynDNS service down? - #3 by peter as advised in another thread.
You will need to bring your own domain, if you need to be able to change NS records. (However that only makes sense if you want to split off a subdomain as a separate zone. For the domain itself delegation needs to be handled by your domain registrar.)