Pop Up

It looks like there's a program running on your computer that embeds Flash Player.  Flash Player reached it's End of Life on December 31, 2020.  As of Jan 12, 2021, Flash Player only loads content that's explicitly allowed (this is typically used in the context of large enterprise organizations with hundreds or thousands of computers and long-term Flash dependencies). 

The icon you're seeing is letting you know that Flash Player loaded, but that the thing that it was asked to load is not allowed.  If this were happening in a browser (the intended use-case for Flash Player), clicking the button would take you to a page that explains that Flash Player is EOL and that you should uninstall. 

So, there's a program on your computer that's probably pretty old, and it uses Flash Player for *something*.  If I had to guess, I'm thinking Screen Saver or some kind of video player.  (If you figure it out, I'd love to know -- I'll add it to my list of possibilities.)

One way to figure this out would be to launch Task Manager (hit Ctrl-Alt-Del on the keyboard and choose Task Manager), then start killing things one at a time, until the weird overlay thing disappears.  Whatever you killed (that isn't Flash Player) when it disappeared is most likely the right answer.