Today, Microsoft is releasing Windows Server Insider Preview build 20282. There's no blog post to announce it just yet, but it's safe to assume that there's nothing new. This is more likely the RTM build for the fe_release branch.
Microsoft was releasing Iron builds to Windows 10 Insiders all through December, and build 20279 was originally planned to be the RTM build. As it seems, some bugs have been found and Microsoft had to put out a couple more builds. The confusing part is that there isn't going to be an Iron update for Windows 10.
Windows 10 21H1 is likely going to be an enablement package like 20H2 was, or it won't happen at all. One thing that it won't be is a major update like the RTM build from fe_release. Instead, this release is all about the Windows 10X RTM. So while fe_release is happening for Windows 10X, and it's not for Windows 10, it's totally unclear what's happening with the Semi-Annual Channel for Windows Server.
Whatever it is, this is a preview for the next LTSC release as well, which is particularly odd if it's not going to line up with a Windows 10 release. If you want to download it, you can find it here.