Welcome to Android Central! Those apps are probably downloading the videos to their own download directory, and not the main download directory. Use any file manager app to explore, and look for the directories that are associated with those apps. If you find where the files are downloading, see if there's a file called .nomedia -- that file instructs the system to ignore the directory when scanning for media to show in the Gallery. You can try deleting the .nomedia file, but the app might create it again.
Alternatively, look in the FB or Instagram app settings and see if there's any way to select where files are downloaded to.
12-17-2021 12:02 PM