Microsoft officials have said nothing publicly about the next Windows 10 feature update. While there have been sightings of 21H1 references in Insider test builds and some Microsoft documentation, there's been no other official information on the next release.
The Windows 10 2H1 feature update, like 20H2, will behave almost like a cumulative update. Drivers that meet Windows 10 2004 requirements won't require new signatures. Windows 10 2004, 20H2 and 21H1 will all be based on the 2004 code base, the blog post notes.
The reason this is significant at all is because a number of IT pros had gotten accustomed over the past couple of years to Microsoft releasing a larger Windows 10 feature update in the spring, followed by a minor update in the fall. This year, the spring/H1 update will be a minor one. Rumor has it that the fall/H2 Windows 10 feature update will be bigger, in terms of new features. Among those new features are a number of UI and in-box application UI changes that go by the "Sun Valley" codename.
Microsoft officials aren't talking about any of this beyond the aforementioned blog post at this time. The Windows team has not yet released a 21H1 test build to the Beta or Release Preview rings, though that is likely to happen relatively soon.
Once Microsoft finalizes 21H1 after it's tested -- and likely continues to add fixes and updates to it -- it will start rolling out 21H1. The process will likely be like what happened with 20H2. The 20H2 update was meant to be a small update to 2004, activated with an "Enablement Package," which looks and feels a lot like a Cumulative Update. For anyone running a version older than 2004, the 20H2 update updated like a regular Windows 10 feature release -- meaning it won't be quite as quick and painless. (This is the same way Microsoft rolled out Windows 10 1909, which was a minor update to 1903.)