Microsoft VP John Cable explained what’s new in a February blog post:
A Windows insider blog post gave more details on the fixes in 21H1:
It will also improve Robocopy’s performance when copying files that total over 400 MB in size.
A smaller update focused on security performance improvements should mean less download and reboot time, which is never a bad thing. But what about the bigger features we were expecting? Well, these have been delayed to 21H2 when we expect Microsoft to deliver its Windows 10 ‘Sun Valley’ update. So we all need to prepare for a major Windows update and visual refresh later this year!