What are the steps to take when buying a domain name already owned by another party?
You should change the nameservers immediately the domain hits your registrar. Make sure you have the nameservers pointed to some webserver. If you point it to Cloudflare, don’t leave it hanging. Make sure you add the names to your Cloudflare account and point them to an origin server (some webserver) you are pointing to.
Don’t let cyber miscreants hijack your domain name.