Specifically, the update is for Windows 10 versions 21H1, 20H2, and 2004, and KB5004296 will bring the build number to 19043.1151, 19042.1151, and 19041.1151, respectively. You can manually download it and these are the highlights:

• Updates an issue that prevents gaming services from opening certain games for desktop users.
• Updates an issue that prevents you from entering text using the Input Method Editor (IME). This might occur, for example, after startup if you have set the power options to shut down a laptop by closing its lid.
• Updates an issue that plays the sound for selecting something in a game loudly when you press the trigger button on a game controller.
• Updates an issue that prevents power plans and Game Mode from working as expected. This results in lower frame rates and reduced performance while gaming.
• Updates an issue that fails to detect that you are connected to the internet after you connect to a virtual private network (VPN).
• Updates an issue that causes printing to stop or prints the wrong output. This issue occurs when you print using a USB connection after updating to Windows 10, version 2004 or later.

“We are initially taking a measured seeker-based approach to the rollout of the May 2021 Update,”

On PCs running Windows 10 Home and on those Windows 10 Pro machines not managed by IT, 21H1 will be installed only when the user chooses the “Download and install now” option. As Cable noted, of the eligible PCs — those running one of the last two versions, either 20H1 or 20H2 — only a portion will be offered this week’s upgrade at the start. Microsoft has long used a scheme that only slowly expands the pool of potential recipients and will continue that practice this time.

Two months ago, Microsoft urged commercial customers to begin testing Windows 10 21H1 using a release candidate of the upgrade.

On Tuesday, the company told IT admins to start what it called “targeted deployments,” meaning small-scale rollouts to PCs whose users have previously been identified as each upgrade’s guinea pigs.

The upgrade was immediately available through Windows Server Update Services (WSUS), including Microsoft Endpoint Configuration Manager; Windows Update for Business (WUfB); the Volume Licensing Service Center (VLSC); and Microsoft’s download center via the Update Assistant and Media Creation Tool.

Rather than an upgrade composed of numerous new features and functionality, the minor 21H1 combined the code of its immediate predecessor with the intervening fixes, then added a splash, a very small splash, of shiny new things.
Windows 10 21H1 will receive the now-standard minimum support of 18 months, putting its retirement date as Dec. 13, 2022. As it is a first-half upgrade, all editions of the OS, including the priciest and most comprehensive, Windows 10 Enterprise, receive the same amount of support for 21H1.