UC Browser creates a hidden, empty file named .nomedia inside its download folders. The Android Media Scanner respects this file religiously. Any folder containing a .nomedia file—and all its subfolders—will be completely ignored by Gallery apps. UC does this to prevent app cache or thumbnails from cluttering your personal gallery.
Here are the within UC Browser to make downloaded videos appear in your Gallery: uc browser download video not showing in gallery
installed within UC Browser; these often save files to a specific "My Videos" UC Browser creates a hidden, empty file named