If you want to download ISO, you must pretend you are not Windows. Otherwise, it will redirect you to the media creation tool, that will download bunch of files that it wants to hide from you and insist on creating a media for you.
Media Creation tool doesn't download the ISO with CU updates. It downloads one that is about a year old and then once you run Windows Updates, it has about a years worth of updates to install (if not more).
The point was that Windows 10 2004 is RTM but you have to be a MSDN subscriber to download it, or find some shady Russian website to get it from.
Last time I tried, changing your user agent to Safari (OS X) or Firefox (Linux) made the media creation page redirect to a link to download the ISOs. I suppose if you had WSL installed and an X server you could bring up a browser in there, or you could use lynx :P.
AFAIK 2004 is supposed to be released next week, 28th. It is not yet available on partner download site either.