I am unable to hide the file extension names (.avi, .mp4, etc...) in File Explorer. A few weeks ago I checked the 'File name extensions' box under the 'View' tab. Now, when I click the box to uncheck it, the check mark and the files disappear very briefly then reappear (extensions remain).
I took a look at 'Folder Options' from 'Appearance and Personalization' in Control Panel. The only related option I saw was 'Hide extensions for known file types', whose box I checked to no avail. I also tried the 'Restore Defaults' button and still the extensions remain.