Today, Microsoft is releasing ISO images for Windows 10 version 21H1 to Windows Insiders. It's meant for those on the Beta channel, and will start you off at Windows 10 build 19043.
Build 19043 RSS
Yesterday, Microsoft finally announced Windows 10 version 21H1, and as you'd expect, you can start testing it out right now. You just have to enroll in the Beta channel of the Windows Insider Program.
Microsoft hasn't talked about what's going on with Windows 10 21H1, but it looks like the update is still happening, and that it's going to arrive with a small build increment like previous updates.