Windows 11 has plenty of security features built in, and one of them is quite quirky. It is called Smart App Control, and it works by preventing untrusted software from running on your computer instead of detecting and removing malware, adware, or potentially unwanted software post-factum. When you try to run an app, SAC checks it and if it does not show signs of malware or other digital nastiness, give it the green light.
Microsoft positions SAC as a better alternative to typical antivirus software, as it uses fewer system resources. However, there is one interesting thing about it: you cannot turn it back on after disabling it.
When you clean-install Windows 11, Windows Defender sets Smart App Control into evaluation mode. It analyzes the apps you run and determines trusted software. After a few days of use, it switches to Always on mode, and if you want to turn it off (say, to run a certain app that Windows Defender does not like), there is no way to turn it back on. The reasoning behind this design was that a system can no longer be considered safe after shutting SAC down.
This behavior has some obvious downsides. Recently, ASUS ROG Xbox Ally users started complaining about Smart App Control killing the Armory Crate software, which is responsible for managing the console"s hardware. While it was possible to bypass the issue by turning Smart App Control off, that would result in leaving the console less secure. On top of that, reinstalling Windows is probably the last thing a handheld console owner wants to do.
Now, Microsoft is changing how Smart App Control works. The latest update for Windows 11 versions 25H2 and 24H2 makes it possible to enable SAC once again without reinstalling Windows 11 (Microsoft started testing it in December). You can do so by heading to Windows Security > App & Browser Control > Smart App Control. Note that SAC is a Windows 11-exclusive feature that is not available on Windows 10.
It is worth noting that you should not turn Smart App Control off unless you have a solid reason to do so, like running an app you trust that Windows Defender does not want you to run. Or, as was the case with the ASUS ROG Xbox Ally, when you encounter a false positive. For everyone else, keeping Smart App Control running is the safest bet.