The latest Windows 11 Dev build contains a new Spotlight theme, but for some reason, it is not available for all Windows Insiders yet. Here is how you can enable the new theme using the Vivetool app.
Build 22000.829 (KB5015882)
Windows 11 in Release Preview adds urgent notifications bypass and more
windows 11 insider preview
Windows 11 released to Dev Channel and ISO comes with File Explorer tabs
windows 11 promo