How to prevent the User to login only on his Computer and no other Computers

You cannot enforce workstation-specific logon restrictions through Group Policy directly. The supported way in Active Directory is to configure the Logon Workstations property on the user account in Active Directory Users and Computers, which you already showed. That setting is stored in the userWorkstations attribute and is evaluated by the domain controller during authentication. GPO does not provide a native policy to restrict logon by workstation because it is account-specific, not machine-wide.

If you have many users and computers, the scalable approach is to script or automate the modification of the userWorkstations attribute via PowerShell or LDAP, for example using Set-ADUser -Identity Dummy -LogonWorkstations Adamix. This way you can apply the restriction in bulk rather than manually editing each account. Another option is to use security groups and assign workstation-specific permissions, but the cleanest method remains managing the userWorkstations attribute programmatically. In short, GPO cannot do this; automation through AD tools is the best practice.