Microsoft veteran engineer Raymond Chen has shed light on the “app is preventing shutdown” warning that can prevent users from shutting down their PCs. According to Chen, when a program detters the shutdown process, Windows presents a window known as the Blocked Shutdown Resolver (BSDR), which displays information about the processing windows and other windows waiting in line.
However, there’s an instance where the program fails to call the necessary function, resulting in a generic string like “This app is preventing shutdown.” In some cases, the description may appear blank. Chen explains that this is by design. Programs often create windows that were never meant to be shown to users, leaving their titles blank.
These dummy windows are designed to receive messages or serve as an anchor for positioning another window. The Blocked Shutdown Resolver shows a title explaining the unnamed program preventing a shutdown. According to Chen, this concept was intentional, and the mystery behind the mysterious window is now solved.
Source: https://www.windowscentral.com/microsoft/windows/mystery-of-the-unnamed-program-blocking-windows-shutdown