It is possible to resolve a hostname to an IP address via the 'nslookup' command (nslookup <hostname>). This IP address can then be used to restrict access through firewall rules. However, keep in mind that applications like Youtube, Facebook, and many others, have numerous associated domains, making it difficult to block access to these applications entirely.
Since you want to allow access to only one specific web page, you will need to create two firewall rules. The first rule should allow traffic to the particular web page, and the second rule should block all other traffic. It's important to place the first rule above the second rule. This ensures that traffic destined for your web page matches the first rule and is allowed, while all other traffic that doesn't match the first rule will be dropped by the second rule.
If you want to restrict access to all devices, you can consider using a Web filter functionality on our devices. This way, you can restrict access based on the URLs. You can find more information about Web filter here and some troubleshooting information here.