Some users have discovered a bug in update KB5012643 that may cause the following issues.
Microsoft: After installing KB5012643, some .NET Framework 3.5 apps might have issues or might fail to open. Affected apps are using certain optional components in .NET Framework 3.5, such as Windows Communication Foundation (WCF) and Windows Workflow (WWF) components.
For now, Microsoft provides the following workaround:
To mitigate this issue, you can uninstall KB5012643. To do this, select the Start button and type, Windows Update Settings, and select it. On the Windows Update settings window, select View Update History then select Uninstall Update. Find KB5012643 in the list and select it, then select Uninstall.
If you cannot uninstall KB5012643, you can also mitigate this issue by re-enabling .NET Framework 3.5 and the Windows Communication Foundation in Windows Features. For instructions, please see Enable the .NET Framework 3.5 in Control Panel. Advanced users or IT admins can do this programmatically using an elevated Command Prompt (run as administrator) and running the following commands:
- dism /online /enable-feature /featurename:netfx3 /all
- dism /online /enable-feature /featurename:WCF-HTTP-Activation
- dism /online /enable-feature /featurename:WCF-NonHTTP-Activation
Microsoft is working on a resolution and will provide an update in an upcoming release.