Domain ownership is recorded in domain records (owner record, domain administrator record). These records are filled in by the registrant when purchasing a domain. These fields can always be changed from the registrant's "account" and this is sufficient to change domain ownership (go link).
The domain transfer process does not explicitly change ownership, as the relevant ownership fields remain the same. Only the website and/or registrant's account changes during the transfer. Changing an account can be done on the same registrar's website, and it is not necessary to transfer it to another registrar. If you have purchased a domain on our portal and want to transfer it to someone else with full ownership rights, you can transfer the domain to someone else's account and have the legal records changed there by them. To do this, you can write to our system - in your admin, menu "Support": specify the domain to be transferred and whose account you want to transfer it to: e-mail, name, company. This user must also write to us in the same way from his account, so that the agreed domain: .... is transferred to his account. Based on these letters, our service will transfer the domain to the new account. After that, the new user will have access to the legal records of the domain.