Microsoft has released the first ISO install image for Windows 10 Insider Preview in 20H1 development branch. It’s the Insider Preview build 18912, that is offered for download.
Brandon LeBlanc, Senior Program Manager at Microsoft on the Windows Insider Program Team in WDG, has announced it a few days ago.
FYI for #WindowsInsiders asking for ISOs – we’re shooting to provide the ISOs for 20H1 Build 18912 early next week.
— Brandon LeBlanc (@brandonleblanc) 6. Juni 2019
Now Windows Insiders may be login to their account and download the ISO images for Windows Insiders Preview build 18912 of Windows 10 20H1 from this Microsoft page.