How to determine if a domain is busy without whois services?

Question

Domain Name System

Subject.
Is there a way?
It is also necessary for the method to work with domains that are registered but not available (no dns records)

Answer 1

whois is the only database that stores information about registered domains. The dns zone configuration is based on the whois database, roughly speaking.
If you refuse to use whois - you give up the only reliable tool.
PS. You can flip a coin ;)