Hi Eslam,
The "Enroll now" button is missing because your activation channel is set to Retail.
The Windows 10 Extended Security Updates (ESU) cloud enrollment option via the Windows Update settings page is strictly reserved for commercial customers. This means your device must be managed via a Work or School account (joined to Microsoft Entra ID or an Active Directory domain) and utilize volume licensing or enterprise management tools like Intune.
Since your machine is an independent personal device on a retail license, you cannot enroll directly through that menu interface.
To proceed, you will need to register your device and purchase an ESU license key manually through an authorized Microsoft Cloud Solution Provider (CSP) partner once consumer options become available, rather than using the built-in settings button.