https://www.bleepingcomputer.com/news/microsoft/how-to-download-the-windows-10-21h1-iso-from-microsoft/

With today's release of Windows 10 21H1, otherwise known as the May 2021 Update, Microsoft has also released new ISO disk images for the operating system.

If you want to perform a clean install of the operating system on a new machine or run into a problem, it is always helpful to have a copy of the latest Windows 10 media available. This article will explain how you can download the Windows 10 21H1 ISO directly from Microsoft's servers.