It's the green squircle on the last row, it appeared a few days ago. It cannot be deleted, and it does nothing.
I've checked all the .desktop files under /usr/share/applications and /home/user/.local/share/applications, they all have a Name property.
I have uninstalled the most recently installed apps in case one of them had something to do with it (though I had nothing exotic, most non-store apps we're from this forum), but it didn't help.

Can anyone help with what can I do to find out where does this icon comes from?
Thank you.