We have been using a domain for a considerable period of time, but it was registered a long time ago and the original registrant cannot be located.

The whois information indicates that it belongs to a private individual, and the only information we have been able to obtain is their full name.
Is there any method to obtain more comprehensive information?

Typically, one can resolve the issue of an absent administrator and the need to update login credentials for the admin panel by making a phone call or sending a written request to the technical support or management of the registrar or hosting company.

It is necessary to provide evidence of recent payments for the domain or hosting with the company seal. As someone who has worked in hosting, such requests were a regular occurrence, at least once a week.

If the host registered your domain and you plan to renew it through them, submit a ticket requesting to transfer the domain to another registrar. The host will specify which documents are required, potentially including a passport scan.
It's advisable not to keep domains with the host to avoid potential conflicts or non-standard situations. This way, if any issues arise, the site can be restored from backup while you focus on the domain separately.

Generally, the only way to obtain a domain is to search for the person who owns it and request a transfer from them.
In certain cases, legal action may be an option, but this is a difficult process that typically relies on existing trademark ownership. Obtaining information on domain owners has become more challenging following the implementation of 152FZ.

Communication with registrars or official requests from eligible organizations are the main methods of obtaining this information. Some registrars may offer a private mailbox to contact the domain owner, which can facilitate the transfer process to the address registered with the domain.

In cases where the whois information of a domain indicates that it belongs to a private individual, and the original registrant cannot be located, obtaining more comprehensive information can be challenging. However, there are several avenues that can be explored to gather additional details.

1. Contact the Domain Registrar: Reach out to the domain registrar listed in the whois information. They may have processes in place for handling requests related to privacy protection services that could potentially help in obtaining more comprehensive information. Some registrars offer services where they act as an intermediary and forward legitimate requests to the domain owner while maintaining their privacy.

2. Legal Action: If there are legal or policy reasons necessitating the disclosure of the domain owner's information, legal action can be pursued to compel the domain registrar to reveal the identity and contact details of the domain owner. This typically involves filing a legal request, such as a subpoena, through the appropriate legal channels.

3. Domain Privacy Services: Some domain privacy services provide a layer of anonymity for domain registrants. However, these services may still maintain records that could be subpoenaed if legal action is pursued.

4. Professional Investigative Services: Engage a professional investigative service or a private investigator specializing in digital domains. They may have access to additional tools and resources for uncovering information about the domain owner.

Legal and ethical implications of accessing private information vary by jurisdiction, so it's crucial to seek legal counsel and ensure compliance with applicable laws and regulations when pursuing additional information about a domain owner.