Microsoft released Windows 10 cumulative update KB4489899 yesterday, and in addition to the usual bug fixes and security improvements, the update is supposed to address the performance issues in certain games that were caused by its predecessor.
That update, KB4482887, was released on March 1. Its primary focus was to bring the Retpoline mitigation to the Spectre Variant 2 vulnerability to Windows 10 to improve performance over previous mitigations. But it also caused low frame rates, mouse input lag, and other problems in games like Destiny 2.
The issue appeared to affect people who updated to KB4482887 regardless of their hardware configuration, installed drivers, or other factors. Deleting the update also fixed the problem, so it was clear that the blame lay squarely on Microsoft's corporate shoulders. (Or at least those responsible for Windows 10 updates.)
But now KB4489899 is said to fix the problem. Microsoft said in the release notes that this update: "Addresses an issue that may degrade graphics and mouse performance with desktop gaming when playing certain games, such as Destiny 2, after installing KB4482887." It also improves HoloLens and has security updates.
KB4489899 does have issues, though. One causes "applications that provide advanced options for internal or external audio output devices" to stop working on "machines that have multiple audio devices." Microsoft listed Windows Media Player, Realtek HD Audio Manager, and Sound Blaster Control Panel as examples of such apps.
That problem has a temporary solution, which involves selecting the "Default Audio Device" in the app's options and then sending the app's audio to the right device using per-application audio settings in Settings > System > Sound > App Volume and device preferences. Microsoft plans to fix the issue in late March.
Hopefully, that issue--along with the others listed in the release notes--isn't a deal breaker. If it isn't, KB4489899 should be good to go for people who didn't want to sacrifice in-game performance by installing KB4482887. The update and its requisite service stack updates can be installed, fittingly, via Windows Update.