Once you have the ISO file, you cannot just copy it to a USB drive; it must be made bootable.
Get-FileHash C:\path\to\Win10_2004_English_x64.iso -Algorithm SHA1 windows 10 2004 download
Since version 2004 is no longer the current release, you will not see it via the standard "Check for Updates" button. You have two primary methods to acquire the installation files. Once you have the ISO file, you cannot
If you need a clean install, an ISO file is the best route. While Microsoft removes old ISOs from the main download page, they archive them. Once you have the ISO file