Windows 11 users may want to pause one of the more recent preview updates that is causing problems for .NET Framework 3.5 applications. Thankfully, there are several workarounds to this problem, but for now your best bet is to probably avoid the KB5012643 preview for now.
Microsoft has acknowledged the issue (via BleepingComputer (opens in a new tab)) in the status update on the official Windows 11 documentation (opens in a new tab). It says the problem is limited to users running the 21H2 version of Windows 11 with the KB5012643 update installed, and means that apps using the .NET Framework 3.5 may not work properly or even work properly. can not open.
This appears to be affecting specific components in the framework, so not all applications will be affected. It seems that apps that work with optional features like Windows Communication and Windows Workflow Foundation on framework 3.5 are most likely to crash.
This can include a lot of console applications and things like Windows services. Microsoft hasn’t provided a list of the specific apps affected, so it’s best to assume this could affect a wide range of programs.
Microsoft recommends that you uninstall the update if you have any problems. You can get there by going to Windows Update Settings in your PC’s System Settings. From there, you’ll be able to view your update history and rollback to a previous version.
If not possible, another fix is to re-enable .NET Framework 3.5 and Windows Communication Foundation in Windows Features found via control panel. Microsoft has more instructions on how to do this (opens in a new tab), but scrolling back is probably the easier and more complete fix if it’s available to you. At least that 40 minute boot time bug is fixed (opens in a new tab).
Of course, Microsoft is working to solve this problem instead of just offering alternatives. The .NET Framework 3.5 is set to provide mainstream support for another two years, with five years of extended support after that, so it’s not going anywhere anytime soon.