Hi, I am an independent advisor and welcome to Microsoft Q&A.
Let me help you with this issue.
On your keyboard, tap on ALT F4 to close the active window in front of your screen.
Open Task Manager, by right-clicking the taskbar, go to the Details tab, and close all active browsers.
Please let me know if that works. If not, restart the machine by right-clicking the Start menu and choosing Shutdown or Sign Out, then choosing Restart. If in case you still see the pop-up, it must be an application already installed on your machine. Please take a screenshot and paste it here. Thank you!