Hi and thanks for reaching out. My name is William. I'm a Microsoft Windows Certified Professional and Systems Administrator. I'll be happy to help you out today.
Microsoft does not make older feature updates available for public download. You will need to use a utility like Rufus to download the 2004 ISO. This link contains details (although it eludes to 1909, the same steps still apply): https://pureinfotech.com/download-windows-10-19...
That said, 20H2 is not considered a major update from 2004. Have you confirmed that 20H2 can run the program in question?
Disclaimer - The above link is not a Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.