Windows 11's KB5012643 update is proving to be quite troublesome. After Microsoft issued temporary mitigation for the issue where it might cause Safe Mode to not work right, the company has also now updated the Windows 11 known issues page with another problem. This time, it is one relating to issues with apps that use .NET Framework 3.5.
Per that page, NET Framework 3.5 apps that use using optional components such as Windows Communication Foundation (WCF) and Windows Workflow (WWF) might fail after installing OS Build 22000.652 or KB5012643. As Neowin points out, not every NET Framework 3.5 app is impacted, but there is a workaround that Microsoft suggests that could divert any issues.
Naturally, it is to uninstall and remove KB5012643 from Windows 11 through the Windows 11 settings app. In the event that you, for some reason, can't remove this update, Microsoft suggests re-enabling .NET Framework 3.5 and the Windows Communication Foundation in Windows Features. This is for advanced users only, as it requires running these prompts in an elevated command prompt.
dism /online /enable-feature /featurename:netfx3 /all
dism /online /enable-feature /featurename:WCF-HTTP-Activation
dism /online /enable-feature /featurename:WCF-NonHTTP-Activation
For now, this bug has just been tagged as "mitigated" by Microsoft. That means it is just a temporary workaround. You'll have to keep an eye out for a future update that fully addresses the issue. Microsoft says it is working on a resolution and will provide an update in an upcoming release.