Microsoft just released Windows 11 Insider build 25267 to the Dev Channel, the last new build before the new year. The build comes with ISOs, so if you prefer to clean install this build you can.
In this build Microsoft continues to tinker with “different treatments for how search looks on the taskbar,” and if you’re seeing the more rounded corners, you can right click on the taskbar, open taskbar settings, and play a bit with the way the search bar looks.
There’s quite a list of fixes for this last build of the year, you can check them out over at the Windows Insider blog post.
