Microsoft officially started rolling out Windows 10 version 2004, the Windows 10 May 2020 Update yesterday. For many people, the update is not being offered when they check via Windows Update. Windows 10 Update Assistant is a tool that lets you perform an upgrade to the latest feature update immediately after it is installed. The Media Creation Tool is a Microsoft utility that allows you to create a bootable USB, DVD, or ISO that can be used to install Windows 10. The final method is to download a Windows 10 2004 ISO and burn it to a USB drive.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-2004-update-not-offered-heres-how-to-get-it-now/