In Nautilus, one can use the search function to search for parts of filenames, e.g. ".mkv" or ".jpg".
Let's say I have a media directory filled with image files and video files all of different formats. How can I search using a GUI file browser for files that are, say, video files (so .ogg, .mkv, .mp4 and so on) or files suited to being opened by default by a video player application?
pcmanfm
, the gui file manager default in Lubuntu 18.04 and previous, has an option on the menu View / Sort Files / By File Type that provides this functionality.