Open File Explorer with Ctrl+e and click the View button towards the top left. There you can select File name extensions.
The method is similar to the one in Windows 10 but it’s not in the menu behind the View button. You can find it by clicking on the File button.
Open File Explorer with Ctrl+e and click the Organize button on the top left of the window. Select Folder and search options from this menu. After this you can click on the View tab in the window that will open automatically. Here you can find a check box for: “Hide file extensions for known file types”