https://www.bleepingcomputer.com/news/microsoft/how-to-download-the-windows-10-2004-iso-from-microsoft-now/

Microsoft announced last week that the Windows 10 2004 build 19041.207 is the final RTM version and will be released next month as the Windows 10 May 2020 Update. For those who want to download an ISO and perform a clean install of Windows 10 2004 before it's released, you use the following instructions.

For those not familiar with an ISO image, they are sector-by-sector copies of a DVD that are stored in a disk image file. This ISO file can then be written, or burned, to another DVD to create a replica of the original, mounted as a drive letter in Windows, or extracted by a program like 7-Zip to access the files contained in it.