I am also having issues with this. I created an account just to chime in.
I have been using CCleaner for a very long time and this past week is the first time I have seen this. Like others have stated, the application windows opens up every time a game closes. It happens with Steam games, Epic Games, and games with standalone installs.
It doesn't seem to happen with all applications though. Closing Chrome, Blender, and various other applications does not trigger it.
Most recently, I have closed Rogue Company (Epic Games Launcher), Hell Let Loose (Steam Launcher), and Escape f