Beginning with Windows 10 version 2004, the option is no longer there, and Microsoft explains that it’s all because of the automatic push of new feature updates that only happens on devices running OS versions that approach the end of support.IT admins that still need to defer updates can achieve the same effect via group policies:
“Update less: Last year, we changed update installation policies for Windows 10 to only target devices running a feature update version that is nearing end of service. As a result, many devices are only updating once a year. To enable all devices to make the most of this policy change, and to prevent confusion, we have removed deferrals from the Windows Update settings Advanced Options page starting on Windows 10, version 2004,” Microsoft says.
“If you wish to continue leveraging deferrals, you can use local Group Policy (Computer Configuration > Administrative Templates > Windows Components > Windows Update > Windows Update for Business > Select when Preview builds and Feature Updates are received or Select when Quality Updates are received),” the company explains.Users who already want to update to Windows 10 version 2004 can manually force the update via clicking the "check for updates" button in Windows Update. The large-scale rollout of Windows 10 version 2004 is expected later this summer.