I usually find the owner has a dual display set up and they are currently on one display. Either change back to a single display or go fishing for the app like you read at https://answers.microsoft.com/en-us/windows/forum/windows_10-files/file-explorer-will-open-but-will-not-show-up-on-my/fc6419fe-06dd-4e56-95aa-2528d14369a5?page=2 (which is hard IMO.)
It shows on the task bar. When I cascade or show side by side or maximize from task bar the windows it still won't show

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic