KB5015878 is aWindows10, will not automatically download or install on your device unless you manually check for updates and then click the Download & Install button below the clearly worded Optional Updates section.
This optional update comes with some new features. For example, users can now receive important notifications when Focus Assist is launched. Focus Assist is a feature similar to “Do Not Disturb Mode” on your Android or iOS device that hides annoying notifications when you want to stay focused.
Another new addition is dedicated to enterprise customers. Microsoft notes that it has enabled “recovery” for Windows AutoPilot deployment scenarios. Likewise, the update improves the OS upgrade experience as well. Microsoft also fixed an issue that caused continuous video clips to play.
In an updated support document, Microsoft states that the input indicator and language bar may not appear in the notification area. The bug has been included in the official log of the KB5015807 update, but so far not many people have reported the problem.
Microsoft has fixed the issue with a server-side update that simply shuts down the code change that was causing the problem. Since it’s a server-side update, it may take up to 24 hours for your device to get the update. After getting the update, the user needs to restart the device to deploy.